This tip was submitted by Barry Bieber Glasair II-S RG
If you’re trying to build a showplane, don’t bother trying to use allen head instrument bolts on a painted surface. The sharp edge on these bolts chip the paint, even with only a two-finger torque! That’s 1-2 inch-ounces? I have washers under the bolts on my panel. I’m not sure if anyone noticed, but they are only .010″-.015″ larger than the O.D. of the bolt head. If anyone needs #4 or #6 washers, I think I have thousands now! But I had to look high and low for #4 and #6 washers that did not have too large an outside diameter.
For the 6-32 screws, find a hobby shop that is into model trains and ask for Kadee insulating washers (P/N 209). They come in gray or red. Their use is for model train wheel spacers. The company address is Kadee Co., 673 Avenue C, White City, OR 97503-1078. The dimensions of these washers are .125″ I.D. x .250″ O.D. x .010″ thick. I’m not sure what they are made of. They are rather soft, almost like a thick paper or thin cardboard material. I did a number of tests on painted surfaces with great results
Now, for #4 washers for 4-40 screws. Vision gauges use #4 screws. Finding these washers wasn’t so easy! After purchasing #4 washers that were too big from all types of retailers, the light came on, and I looked through the hardware left over from my RC/ modeling days. I had twelve fiber washers that fit perfectly under the #4 screws, with only a very slightly larger diameter than the head of a hex bolt. After trips to hobby shops to no avail, I called fellow modelers from the past. After calling three different modelers, I was able to obtain enough for my panel.
We were finally able to determine what the original use of these washers was. They were sold by a company called Kraft that made R/C radios, servos, etc. (No! Not cheese!) These washers were available in a Kraft servo mounting kit. It came with screws, grommets and washers. This company has been out of business for a number of years, but you could possibly find leftover hardware kits at a local hobby shop or go to a local R/C flying field and ask around. Some of the old timers are likely to have some lying around.