Strippers can be expensive. Terminate thinking rap stars, lap dances and sports celebrities. We are talking nigh a "stripper" in terms of a hole that has had its threads stripped out or damaged. In improver to being expensive to repair, strippers also require a great deal of time and normally evoke a great bargain of frustration. Fortunately, understanding the history of the materials being threaded along with the science of inserts can aid you lot avert encountering a stripper or, at least, be prepared to select the correct parts to repair a stripper. Done correct, you'll never have a thread failure in the aforementioned pigsty over again.

Text and Photos by Michael Ferrara // Illustrations by Paul Laguette

DSPORT Issue #166

Difficult Times

Forty years ago, the earth was a harder place. Your grandparents weren't lying to you. Cast-iron alloys and steels were the bones building blocks for just nigh anything. On the automotive side, grey cast iron was the "go-to" material for engine blocks, cylinder heads, manifolds, housings and heavy brackets. Steel was the textile of choice for smaller brackets, fasteners and the frame and torso of the vehicle. While the mechanical properties (forcefulness, stiffness, touch and corrosion resistance) varies immensely beyond different grey cast iron and steel alloys, they all have one thing in common. For the most part, these materials, when used on components that take threaded holes, are all on the "difficult" side with Brinell Hardness ratings (HB) in the 150 to 300 range (tool steels can get upward to 900 on this scale). Being difficult in nature, grey bandage fe and steel will tend to accept exceptional thread strength and thread retentiveness capabilities as long as these materials are protected from corrosion. When thread damage does occur in cast fe and steel, the most mutual exercise is to drill out the existing threads and tap the hole to accept a larger fastener. In many cases, this solves the trouble. When the aforementioned size fastener must exist used, an insert tin be installed to save the day.

Going Soft

Today, it's not just "emo" millennials that are softer. We alive in a softer world. The materials that have replaced grey bandage iron and steel are relatively so . The earth has moved from the Steel Age to the Aluminum Historic period. Pure aluminum will only hit fifteen on the HB scale, whereas aluminum alloys can range in hardness from xx-to-150. The aluminum alloys used on almost of the sand cast components in a vehicle are typically in the 45-to-65 range in terms of hardness. The highest hardness cast-aluminum alloys are used in cake and cylinder heads. These will typically have a range of hardness from 75-to-85, about the same as 6061-T6. But 7075-T6 aluminum blend has a hardness of 150 which is on par with greyness cast iron.Inserts

Hard Commodities Meets Soft Threads

While the materials where threads live have become softer, the materials used for fasteners accept in many cases become harder. In fact, some of the super-alloys used in high-performance head studs and rod bolts have hardness levels approaching that of tap (every endeavour to drill out a cleaved tap?). As a upshot, it's no surprise that strippers are more mutual than ever earlier. Since virtually of the threads on today's vehicles are fabricated of materials with just 1-third to one-half the hardness of grayness cast iron, it's no wonder that more than threaded holes experience thread impairment than e'er earlier. It's been said, "If a threaded hole in a softer metal uses a fastener that is installed and removed on a regular basis, a harder-material insert is a must." Unfortunately, the cost and time involved with installing inserts at an OEM level means that information technology will never happen on a large calibration. In that location may exist a few key, high-stress locations in an engine block or interruption component, but 99 percent of all the threaded holes volition not come from the manufacturing plant reinforced with an insert.

The Solution

If every single aluminum component in the world could be manufactured from 7075-T6 aluminum alloy (which has equal hardness to typical gray cast iron alloys), the number of strippers in the world could be brought dorsum down to the Steel Age numbers. Due to the high-cost of this material and the need to bandage sure parts, this will never happen. Instead, the solution for stripped threads are inserts.

Insert Tech 101

Thread-repair inserts come in a variety of materials and in a myriad of designs from domestic and overseas manufacturers. Timed thread body inserts, wire coil inserts and keyed inserted brand up the iii major families of thread inserts y'all'll probable meet. Each blueprint has its claim and may be superior to some other based on upkeep, installation fourth dimension, maximum O.D. permitted and the necessary strength of the repair or upgrade. So which type of insert is best? Information technology all depends on the grading criteria and the application. Here's an overview of the 3 primary types in order of popularity.

HeliCoil Helical Coiled Wire Inserts

Band-aid is a brand synonymous with bandages, while Heli-Coil is a brand synonymous with thread repair inserts. Encounter a stripper and the solution is often touted every bit ,"but HeliCoil information technology." HeliCoil and the similar designs inspired by this pattern are available from a number of other companies. It'due south the thread-repair solution most probable to exist found at local auto parts stores. HeliCoils were originally made from square, stainless-steel wire wound and so that the wire had a diamond profile that would fit into the repair threads. When installed into the larger repair threads, the wire forms a gear up of threads engineered to meet the original dimension of the stripped-out hole. The repair threads for the HeliCoil insert are made by using a Screw Thread Insert or S.T.I. tap. This is the same blazon of tap used for some other inserts. An S.T.I. tap uses a simple but somewhat misleading naming convention. An Southward.T.I. tap is actually about xiv percent larger in diameter than a standard tap of the aforementioned designation (M10x1.25 versus M10x1.25-S.T.I.). HeilCoil used to fix a damaged thread Here's how it works for an M10x1.25 thread repair. Get-go, y'all would drill the hole with a 10.25mm drill (a standard M10x1.25 thread would employ a much smaller 8.75mm drill). Then you lot would utilise an M10x1.25-S.T.I. tap. This S.T.I. version of the tap will have a major bore of up to xi.787mm, whereas a standard M10x1.25 tap is about 1.5mm less in bore. Once the hole has been drilled, tapped and cleaned for the repair insert, the HeliCoil insert is screwed into identify with the installation tool. Once the insert is located in the general vicinity of the desired location, the tab is broken off to secure the insert in place. In addition to beingness the most popular and readily available thread insert, HeliCoils also require the minimum amount of oversizing to the hole (same every bit Fourth dimension-SERT), provide a corrosion resistant thread fabric, and evangelize the least expensive solution (about the half the cost per insert compared to TIME-SERT and simply one-fifth to ane-twenty-fifth the toll of Keenserts). On non-bullheaded, through-holes, HeliCoils tin can besides be installed from the behind of the hole making it the only solution in some situations. [table id=1 /] While HeliCoils may be one of the better choices for repairs that are not under farthermost stress, strains and vibrations, information technology does have its shortcomings. First, since the insert is not a unmarried continuous piece, installation tin sometimes be slightly challenging compared to solid-body inserts. In addition, the discontinuous nature of the insert means that using an anaerobic thread locker means that both the insert and the fastener screwed into the insert are both going to get the thread locking compound whether that's your intention or not. When a repair is beingness made on the vehicle, special attention must likewise exist exercised to ensure that the locking tang doesn't become a foreign object that falls into a critical area. Finally, the forcefulness of a HeliCoil repair has been demonstrated to be less than a solid trunk insert. Nosotros hope to examination a number of different thread repair insert designs in the hereafter to requite this a more definite number. Time Sert vs Keensert diagram

This illustration displays the difference betwixt Fourth dimension-SERT inserts which sync the outside and inside threads with each other versus Keenserts that do not sync outer and inner threads, which leads to inconsistent wall thickness and the demand for a larger O.D. sizing of the insert.

TIME-SERT Timed Solid Torso Insert

While not also known to the mainstream, Fourth dimension-SERT and the family of solid trunk inserts are many mechanics number one choice for thread repairs in loftier-preload fastener applications. This solid body thread repair solution uses a solid carbon steel or stainless-steel continuous insert that has the exterior and inside threads in sync or (in fourth dimension) with each other. By keeping the threads lined up on the inside and outside of the insert, the cross-sectional-area or wall thickness can remain consistent. The effect is the ability to maximize strength for a given outside bore of insert. TimeSert Fourth dimension-SERTs utilize the aforementioned drill and tap requirements equally HeliCoils, equally both utilise S.T.I. taps. Installation is similar, but in that location are a few fundamental differences due to the deviation in design. Outset, TIME-SERTs use an oversized locating flange on the summit stop of the insert. Hence a combination drill/counter-boring tool or a drill and dissever counterbore must be used. This flange allows the thread to be repeatably located or positioned at a specific location (something that cannot exist accomplished with a HeliCoil or Keenserts). 2d, there is no tang for locking. TIME-SERTs use a special tool to lock the bottom threads into the threaded repair hole. Since TIME-SERTs are a solid body, thread locking compounds tin exist used on the inserts outer threads for additional strength without it affecting the inside threads and fastener. While Fourth dimension-SERTs offering advantages over other thread repair insert designs, it also has a few drawbacks. First, information technology's about twice the cost of a HeliCoil per insert. 2nd, it must be installed directionally, as its flanged-design requires the non-flanged side to be threaded in showtime. On through holes, information technology can be used by installing information technology from either side. On bullheaded holes that are non deep enough to provide enough room for threads and the flange, the flange side can be milled or filed off al later on. Withal, if at that place were only one design of insert that we'd take admission to for all thread repairs, we'd probably select Time-SERTs. Fourth dimension-SERTs deliver the highest strength with the least amount of intrusiveness with regard to the size of the repair threads versus the original threads. Fixing a damaged thread

Once the pigsty has been drilled and tapped with the Southward.T.I. tap, ane) the TIME-SERT installation tool gets a drop of oil before 2) the TIME- SERT is threaded onto the tool. 3) Threadlocker tin can exist practical on the outer threads and 4) inserted into the hole to be repaired. When the insert'south flange bottoms out 5) it as well locks the bottom threads in identify. 6) Remove the insert tool and the 7) TIME-SERT repaired hole is fix.

Keenserts Keyed Threaded Torso Repair Inserts

Keenserts are very thick-walled, solid body thread repair inserts with retaining keys. While a Keensert looks to be very like in blueprint to a Fourth dimension-SERT, there are major differences. While both are solid torso designs that are flanged (requiring counterboring for installation), Keenserts do not have the inner and outer threads "timed" with each other. In fact, a Keensert may have an outer thread with an entirely dissimilar thread pitch than the inner. Dissimilar thread-repair inserts that require Southward.T.I. taps, Keenserts utilize standard taps that are 2 steps larger than the original threaded hole. This means that an M14x1.5 tap would exist used for a M10x1.25 thread repair insert. As such, the amount of material that must be drilled out and the size of the tap are both considerably larger than what is required for a HeliCoil or TIME-SERT repair. Time Sert vs Keensert

To retain the insert, TIME- SERTs use a flange up top and a swedged fit at lesser, while Keenserts use 2 or four stakes.

For an M10x1.25 thread repair with a Keensert, a 12.5mm drill would exist used for the M14x1.5 tap. The M14x1.5 tap would take a major diameter up to fourteen.4mm (an M10 repair with an Due south.T.I. tap would simply have a 11.787mm major diameter). That's a much bigger hole which can be benign in some awarding where astringent corrosion is prevalent in the original threads. The Keensert would then exist threaded into the drilled, tapped and cleaned hole with the Keensert installation tool. Thread locking compounds tin can be used due to its solid body design. Once prepare in position, the installation tool is then used to drive in the 4 key stakes into position. This provides the ultimate mechanical locking of the insert in place. Hence, this design sports infrequent resistance to vibration. Now the downside. The massive outside diameter of the insert makes information technology unviable in applications where the material around the original threaded pigsty is limited, such equally whatever "sparse-wall" castings. Second, the cost for a standard-steel Keensert is nigh four.5 times that of a HeliCoil and more than double the cost of a Fourth dimension-SERT. If you want a stainless-steel Keensert, the cost goes through the roof existence about 25 times the cost of a HeliCoil.Time Sert vs Keensert

Large-SERT Thread Repair Insert

For applications that will benefit from a large-diameter insert or when you are replacing a standard TIME-SERT, TIME-SERT offers a line of oversized BIG-SERTs that are thicker wall and use an oversized S.T.I. tap. For example, an M12x1.25 Southward.T.I. tap would be used on an M10x1.25 BIG-SERT insert. Different sized taps used for inserts to fix a broken thread

Large, Bigger, Biggest! Here is a comparing of a standard (left) M12x1.5 tap, a M12x1.five Southward.T.I. tap (center) for Fourth dimension-SERT and HeliCoil inserts and a M16 tap for Keenserts (right).

The Bottom Line

HeliCoil, TIME-SERT, Keensert or Large-SERT? We've had the opportunity to use all three designs in real-earth weather. And so which type of insert is best? The reality is that it all depends on the awarding and quality of the installation. We've never had whatever of these inserts fail on us. Are we lucky? Not really. Simply having the knowledge of the strengths and limitations of each design will allow you to select the correct insert for the chore. If y'all are not sure, call the manufacturer and enquire. Time-Sert Kit

The Time-SERT Universal Head Bolt Thread Repair Kit (for get-go time repairs) come up with fixture plate, alignment tool, a drill/counterbore bit, tap, installation driver, metal rule, cease neckband, lube, threadlocker and more than.

Keenserts: Keyed threaded trunk insert

+ Thick-wall pattern delivers highest strength for a given bolt diameter + Uses conventional, easy-to-source taps + Solid design provides piece of cake installation + Solid design allows use of thread locking sealer on outer threads + Flanged design allows for positive location of the threads into the object + Positive locking design with four cardinal stakes provides maximum vibration resistance – Makes the largest hole and requires largest tap bore versus final bolt diameter – Over 5x cost of HeliCoil, Over 2x cost of Time-SERT – Availability: Hardest to source, limited distributors

TIME-SERT: Timed threaded body insert

+ Thin-wall blueprint delivers highest strength for a given repair-tap diameter + Smaller pigsty and tap requirements than "keyed" way insert + Solid design provides easy installation + Solid design allows use of thread locking sealer on outer threads + No weak spots…consistent wall thickness due to "timed" pattern + Flanged design allows for positive location of the threads into the object + Self-locking design – Higher price than coiled thread inserts – Availability: Not available at most automotive retailers – Uses harder-to-source S.T.I.-sized taps

HeliCoil: Helical Coiled Thread Repair Inserts

+ Helical coiled wire design results in smaller pigsty and tap requirements than "keyed" style insert + Well-nigh readily bachelor thread repair solution + Lowest cost thread repair solution + Tin install from backside on through holes – Cannot employ thread locking compounds on coiled insert without affecting inner threads too – Uses harder-to-source Southward.T.I.-sized taps – Tangs can get FOD – Only held in by frictionThree types of inserts used to used to repair a damaged thread