Hello from Wales

I need to make about a dozen cotters to fit the brakes on my 1928 Lea Francis car. I have the necessary taps and die (9/32″ BSF – an odd size I believe is only used for cotters – ?). As the cotters (two per brake) need to be removed when working on the hubs, brakes, axle etc, I need to ensure long life and resistance to damage, so I am thinking of stainless steel, but I need advice on which grade, treatment etc.

As a reminder, each cotter is made from 3/8 round bar, with an angled flat about an inch long to fit snug against the groove on each shaft, and at the narrow end, a (smaller) male thread about 3/4″ long. Removing a cotter means driving it out by knocking on the end of the thread, so to avoid future damage I intend to add an extractor thread on the other (cylindrical) end, made extra long – 5/16 BSF (as 3/8 would be too big to leave room for the spanner). The nuts will be made from 1/4 BSF plain stainless nuts, bored to 6mm clearance, and tapped 9/32 x 26 tpi. The plain washers will be stainless, too.

So, will ‘ordinary’ 3/8 stainless bar serve, or should I seek hard-drawn, or some high-test material? So far as I can tell, the cotters currently on the market are mild steel, and (in case anyone is interested) many of them have a 6mm thread and 10mm nuts, which tend to pull the washer into a cone. Proper sized cotters do exist, but some dealers don’t know what they are selling.

I look forward to suggestions – many thanks in advance.

Tim

PS for those with an interest in WORDS, a cotter-pin was originally named from this type of cotter, used in larger sizes than bicycle versions to hold proper man-sized machinery together when Victoria was a mere twinkle.