Let’s get right down to the basics. The most important group, ofitems, that hold your whole scooter together is fasteners. Nuts andbolts can be very confusing to the novice. The concept of assemblingcomponents held together with socket-head, button-heads, Torx-head,setscrews, elastic lock nuts (Nylocks), flex-nuts, 12 points and capscrews could become a mind-boggling choice. Add to these decisionsthe variations of sizes, SAE, metric, grades, finishes and materialsand the task to choose the proper fastener can become daunting. I’lltry to cut through the minutiae here so you won’t be forced into a4-year engineering degree to understand what type fasteners areappropriate for your motorcycle.
When it comes to hardware, size does matter. Whether you arebuilding a bike from scratch or just replacing some cadmium plated,dull-looking bolts on your Harley for polished chrome ones, Youshould understand how bolts are sized, along with the proper termsfor the different applications and styles.
Here in the USA we use standard types of fasteners, wrenches andtools to install these fasteners. The Society of AutomotiveEngineers, SAE for short, developed these standards early in the lastcentury, so we Americans who use fractions of inches, instead oftenths-of-meters, would all have a common structure to base ourhardware sizes.
This shot shows bolts with coarse and fine threads from left toright.
One of the most common fasteners on your Harley is a 1/4×20 socketcap screw. Now be truthful. Can you go out to your bike right now andpoint out just one 1/4×20 cap screw? Don’t feel bad. There’s a largecross section of guys who can’t point one out either, and some workon bikes everyday. To understand bolt sizes you’ll need is a basicunderstanding of fractions and inches. Experience, working withsockets, wrenches and fasteners helps a lot.
Bolts are described by the diameter of the shaft, or shank, andthe number of threads per inch. So a 1/4×20 socket head cap screw orcommonly referred to as an Allen bolt, is 1/4 of an inch in diameterand has 20 threads per inch. All you need is the length of thefastener or how deep it goes into the material for the finaldimension, i.e. 1/4x20x1-inch is one inch long. If a bolt is tooshort for your application, you won’t have enough thread engagementto properly hold your bike together. Sometimes, if a bolt is toolong, it will “bottom out” and not become tight. It may alsointerfere with other components.
The number of threads-per-inch determines the difference between”Fine” and “Coarse” threads. Both have advantages when chosenproperly. On your American bike there are typical uses for coarse vs.fine threaded fasteners. There are exceptions to these rules, justlike in the English language, but in general, coarse threaded boltsare used to fasten a solid piece, billet or casting. Fine threadedbolts are coupled with nuts on the backside of the pieces. The coarsethreaded fastener has more “meat” between the threads to grip betterin cast materials while the fine thread has more surface area so youcan maintain a higher torque value (tightness) on a forged orhardened nut.
Let’s shift back to our 1/4×20 example. That’s a coarse threadfastener. If you wanted a fine threaded fastener that is a 1/4-in.diameter you would ask for a 1/4×28. Which means it has 8 morethreads per inch than the coarse threaded 1/4×20. This holds truefor all basic sizes of SAE fasteners. For example 5/16×18 is coarsethreaded while 5/16×24 is fine threaded, 3/8×16 is coarse while3/8×24 is fine threaded and so on. Got it now?
Running from left to right again, the first bolt is a flatheadcap screw. The second a socket cap screw. The third is as buttonheadcap screw, and finally, the last, a hex cap screw.
Bolts are also graded, designating how “hard” they are. Maybeyou’ve heard of a “Grade 8” fasteners and wondered what that was allabout. Well, wonder no more. Everything has trade-offs and boltsare no exception. The “harder” bolt you choose, the higher the gradenumber, and the more brittle or “less shear resistant” it becomes.Just because you are using a higher grade, or harder bolt, it mightnot be the appropriate fastener.
Think of bolts as plastic. If you have a softer plastic rod, itwill flex, stretch and bend. If you have a brittle or hard plasticrod, you can pull on it and it won’t stretch or break, but if you putside tension on the hard rod, it will snap with very little effort.These two characteristics are important to remember when choosing abolt. The standard scale of bolt hardness ranges from Grade-2 (soft)to Grade-12 (hard), but a grade 8 is about as hard as you’ll find ona Harley. Make sure you are using the same grade washer as thefastener. If you use a lower grade washer (softer) it will “give” ordeform in time resulting in a loose bolt.
On a standard “Hex-Cap” or bolt with 6 sides on top, kind ofshaped like a stop sign (only different), you’ll see markings on thehead, cap, or top of the fastener. They indicate what grade the boltis. Most of the bolts you will be using on your motorcycle will beeither a grade 5, which will have 3 slash marks on the top, or agrade 8 which will have 5 slash marks cast into the top. Don’t askme why the SAE decided to mark them this way (probably just toconfuse the uninformed).
Other types of fasteners are not marked clearly, so it isimportant to purchase your fasteners from a reputable dealer.Cheaper fasteners are not hardened the same, or might not have thequality to stake your life on. Can you say “imported”? Beware. Theprocess used to add “tensile strength” or to “harden” fasteners addsto the cost. The harder the bolt the more expensive it becomes. Mostof the inexpensive standard hardware at the “Home Improvement” storesare unmarked are grade 2, which are very soft and flexible. They arefine for holding lumber together, but not what you want on your dailyride.
The head or cap of a fastener also determines its style.Different head styles are chosen for ease of installation,accessibility and the ability to take torque or tightness. The mostcommon fastener is a “Hex-Cap” screw. These are the six-sidedstandard looking bolts that you use a box wrench to tighten.Twelve-Point screws are very similar to a hex cap except they havetwice as many points and you’ll need a 12-point sockets or boxwrenches to tighten them. 12- points are commonly used to attachyour lifter-blocks and head bolts on a Big-Twin engine, becausegenerally you can apply a higher torque value to a 12-point fastener.
Socket Cap Screws or Allen head bolts are used all over Americanbikes. They have a cylindrical rod shaped head with a recessed hexin the top (which has six sides) You insert an Allen style wrench init for operation.
Torx head bolts are found on many new Harleys and have a roundedcap with a modified star shaped recessed in the cap for a toolsimilar to an Allen wrench but with more surface area to allow formore torque without stripping the head. A Torx bolt is nearly theopposite of a 12-point cap screw. Torx bolts are also used forquicker assembly in manufacturing situations. They are easy to graspand more stable on the end of the tool installing them, which makesfor a faster installation. They are also well suited for pneumatic(air) tool installation.
Button-Head bolts have a rounded cap top, which also has ahex Allen style socket or a Torx drive socket. Button-Heads are verycosmetically appealing especially when chromed, but do not take wellto higher torque values without stripping out.
Finally, a Flat-Head bolt has a cone under the head, whichrecesses flat into the surface that it mates to. Flat heads are alsocommonly called counter-sunk Allens. Flatheads also use an Allen(trade name) wrench to tighten them. NOTE: The Allen in thedescription of the fastener is describing the tool used to tightenthe bolt, not the style of fastener. There are tons of differentALLEN bolts, to use the commonly misused term. So it’s important tounderstand the difference and the vernacular to select the properfastener.
Now for the tough ones, because it means new tools. One theleft is the Torx cap screw and right, the 12-point cap screw.
Now, the shiny part. Everybody likes chromed bolts. The guys atthe factory in Milwaukee would rather save a couple of cents perfastener, the time it takes for plating and the problems in dealingwith plated fasteners and use cadmium or galvanized bolts just toprevent rust. High quality chrome fasteners are available to replaceyour dull looking ones on your factory machine. One of the topquality US suppliers of chromed and polished hardware isGardner-Wescott, . They have been inthe business of making chromed fasteners for your Harley or Hot-Rodfor decades and have a huge variety of domestic high-qualityfasteners for your appropriate customizing needs.
Chrome is a durable finish until it is exposed to excessivemoisture or salt. If you live by the ocean or in areas where theysalt the roads, you may want to consider stainless steel fastenersthat are polished. Or you might just want to move somewhere moreconducive to custom bikes. The choice is yours. Polishedstainless-steel fasteners are almost (the key word “almost”) asattractive as their chromed steel counterparts. Stainless steel isgenerally a stronger fastener and will not show rust but will dull astime and oxidation takes their toll. The process is much slower thana chromed bolt in a damp salty environment.
Chromed bolts will perform and look great here in the drySouthwest, which is also a great place to live. If you take yourstandard cadmium plated fasteners to your local bumper shop to getthem chrome plated, it usually costs more than just replacing themwith new production-chromed fasteners. If the plating process is nothandled correctly, it may change the hardness characteristic of yourfasteners. In addition poor plating will hinder tool fitment, ormight chip off the fastener during use. The final point that alsobears consideration, when using chromed or stainless-steel fasteners,is the appropriate use of Anti-Seize to avoid galling and binding ofthe bolts when tightening (see Permatex Loctite tech) which mayresult in the use of foul language and tool throwing.
If you are still a little confused and want to replace some ofyour hardware on your bike with chrome fasteners, pull the suckersand take them to a reputable shop such as Surgical-Steeds (moreshameless self promotion). By bringing in your old hardware, as anexample piece, you’ll take the guesswork out of getting the correctfastener and size. If you’re planning on building a bike fromscratch, hopefully I’ve helped you make informed decision on whattype of bolts to choose for your project. Regardless, it’s veryimportant to choose the right fastener and have it installed properlyto insure a safe, good looking ride for the long haul.
Gardner-Wescott sells a variety of fastener sets as wellas sets for engines, drivelines and wheels. If you can get the rightgroup for your project, it takes the constant trips to the store outof the equation.
Remember, keep the rubber side down.
John at Steeds
www.surgicalsteeds.com
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