bolts, a bit of useful info


Staff member
yes I know you probably never bothered to look and don,t really care UNTIL you start having problems, but it really does help if you understand what the limitations are to fastener strength. and in most cases bolts ARE marked to allow you to at least have some idea as to there limitations








most experienced mechanics have a 5 gallon bucket of assorted bolts and screws to fall back on when they can,t locate a fastener they break or misplace, youll need to clean used bolts with solvent and a wire brush, but having a bucket of spare fasteners is nearly mandatory, A visit to a local salvage yard with several wrenches and a bucket and a couple hours time, will generally allow you to collect a wide random selection ate a very reasonable price , now you may not find exactly every bolt diameter and length and thread size but you will generally find youve accumulated a good basic selection



every mechanic should own a decent 12" caliper to measure the length of a bolt,
that may be missing on any particular application.
bolts used on any application, must not bottom out in a blind bolt hole if the bolt bottoms out it fails to clamp firmly
bolts that are not threaded into a blind hole should extend at least two to three times,
its diameter past the far surface too allow a washer and nut to be threaded onto the bolts extended end to supply clamping force.
so the depth of the item being clamped and the threaded area the bolt secures its threads too should generally be at least 1/4" deeper than the length of the bolt used,
and the threads should extend at least 2-3 times the bolt diameter into the threaded area,
before the bolts clamping force is applied to clamp the item being secured.
obviously you can get a rough measurement with the base of the caliper.
and when in doubt select a GRADE #8 fastener,
as they are significantly stronger than average garden variety hardware store bolts. > Measuring Tools > Calipers&utm_content=56248

boltg1. png ... vellon.pdf ... alling.pdf ... 2192?print ... vellon.pdf ... chart.aspx
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Staff member

I bought this book several months ago and found it be very interesting and informative. For the price of $14, you can hardly go wrong.

Threaded fasteners are discussed in detail, including clear explanations of thread sizes, thread pitch, bolt grades, fastener materials, tensile strengths, threaded fastener tightening, explanations of both inch-format and metric-format fasteners, etc., with special sections devoted to engine bolts and studs. The plumbing section provides a clear understanding of specific formats, including AN sizes, explanation of fittings and hose ends, tips on AN hose assembly, fabricating hard tubing lines, flaring, and more. Each chapter provides plenty of clear photos and illustrations. This is a comprehensive guide to the world of fasteners and plumbing, intended to guide both novice and professional street-performance enthusiasts and racers.

The HP Books part number is 1523. The book's ISBN number is 978-1-55788-523-4.

This book is a complete guide to understanding the world of automotive fasteners and plumbing, and is an excellent resource for novices and pros alike. ... 993&sr=8-2


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The Grumpy Grease Monkey mechanical engineer.
Staff member

its amazing how often I've seen guys grab a metric bolt or an SAE bolt and try their damn best to force it into some similar but obviously not matching thread that was never designed to fit it.
if a bolt won,t easily thread you need to find out why! not grab a breaker bar!

if you run into problems, don,t grab a bigger hammer or a longer breaker bar THINK THINGS THROUGH!!!

I was recently asked to figure out why a guy I know could not get his motor mounts to fit correctly, it less that 30 seconds the reason was very obvious,
he had spend a hour trying to use SAE bolts too screw into METRIC bolt threads!
only because he was smart enough to ask for help
was a potentially very costly repair avoided


Thread Checker tools are available from several sources, most experienced mechanics have several in a tool chest drawer


The Combo (Inch & Metric) Thread Checker™ is an accurate and easy-to-use thread identifier for both nuts and bolts. Each individual gauge features a male threaded stud on one end and a female threaded hole on the other. The Thread Checker is especially well suited for distinguishing between similar inch and metric threads. Conveniently assembled onto a wire loop, it's the perfect portable solution! Hang it on your shop wall or store it in your tool box for safe keeping.
The Thread Checker, also known as a Thread Identifier or Thread Verifier is a great addition for any Home, Hobby, or Inventor's Work Shop; Auto, Motorcycle, Marine, ATV or RV Repair Shop; Heavy Equipment Repair Shop, Military Equipment Repair Station, Machine Shop, Fabricating Shop, Assembly Department, Production Department or Quality Inspection Station!
You can rest assured, these tools are made for the long haul. Manufactured from heat-treated carbon steel with the thread sizes permanently stamped onto each gauge, it will take some serious heavy duty use before we get the opportunity to fill your next order. Proudly made in the USA.
Each size has a nut and bolt checker on the same gauge
Thread sizes are permanently stamped onto each gauge (inch in red, metric in white)
Inch gauges are clear zinc plated, metric gauges are black oxide
The individual gauges rotate freely on the wire cable for fast thread verification
Wire cable with loop for convenient hanging
SWTC-26 Size Specifications:
Inch: 6-32, 8-32, 10-24, 10-32, ¼-20, ¼-28, 5/16-18, 5/16-24, 3/8-16, 3/8-24, 7/16-14, 7/16-20, ½-13, ½-20
Metric: M4x0.7, M5x0.8, M6x1.0, M7x1.0, M8x1.0, M8x1.25, M10x1.0, M10x1.25, M10x1.5, M12x1.25, M12x1.5, M12x1.75
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