View Full Version : Q: how to make half-round wire for model cotter pins?

08-07-2005, 01:55 PM
I need some small cotter pins for my Breisch Associated Hired Man hit-and-miss engine. The pins have to fit a No. 60 drilled hole (0.040). I haven't been able to find pins this small, and wouldn't mind making my own. Does anyone have a source for half-round wire that doesn't require me to buy a mile? Barring that, what's a good way to make half-round wire? I seem to recall there was a slick way described in Strictly IC, HSM, or some place like that, but heck if I can find it.


08-07-2005, 02:15 PM
i've seen some REALLY small cotter pins, so i'm sure they're available commercially. have you checked McMasterCarr?

for a 40thou hole, you're only talking 20thou wire (if not 15), could you tell if it wasn't half-round? ie, just making them out of round wire?

if you only needed a few, how about holding some wire up against a belt sander? inspect for consistent sections and cut them out. bend into cotter.


08-07-2005, 02:36 PM
McMaster has these in 0.030" wire:

Not a "standard" cotter pin though....

For something like that, I'd probably try filing a piece of wire to half round and bend them up with needle-nose pliers.

08-07-2005, 02:50 PM
check out


with a recomended hole size of 3/64ths, only 7 thou bigger than the #60 hole you wanted. google is your friend

08-07-2005, 03:05 PM
If I really needed to make those, I'd take some .023 or .030 welding wire, cut off a piece and hold it tight while running it over a fine sanding drum. Should be almost perfect half round and easy to shape.

08-07-2005, 03:27 PM
Thanks McGyver! The Small Parts ones ought to do fine. They didn't turn up in the first few pages of a google search. They must have gotten swamped by all the Tractor & Lawnmower Parts R Us listings containing the term "miniature cotter pins".

08-07-2005, 03:30 PM
just poke'in at ya http://bbs.homeshopmachinist.net//biggrin.gif, I searched for small cotter pins, glad to help.

Rich Carlstedt
08-07-2005, 05:30 PM
I made some out of .030 wire (iron bailing wire-streched, annealled and streched again)
2 inch square (~) aluminum block, super glue 2 .015 shims (feeler gauge stock) with a 1/32 gap between them .
Wrap the wire around the block, in the groove and sand vertically..makes a nice 1/2 round steel wire in seconds

Rich Carlstedt
08-07-2005, 05:32 PM
Sorry the word is "stretched"
Aircraft Safety Wire is also great stuff for this work, as it is soft and bends well

08-07-2005, 05:36 PM
The usual way is to pull round wire through a half-round drawplate, or to pull 2 round wires through a round drawplate.


08-08-2005, 09:38 AM
Wrap wire tightly around a piece of round stock chucked in your lathe. Then, take light cuts until you've machined the wire in half.


08-08-2005, 09:56 AM
"google is your friend"!!! *LOL*

08-09-2005, 02:31 AM
Have a look at this lot, it might be what you are looking for.