Re: Thread pitch questions

[Anonymous]

fine threads used where vibration may be a concern, as fine threaded fasteners are less likely to loosen off from vibration because of the difference in geometry between fine & coarse thread pitches…

or the fastener has to thread into a thin wall.

In this case – perhaps a combination of both.

And heed Frank’s advice on the repair. If you can’t do the Heli-Coil, consider brazing to fill in the holes, then re-drill and tap to original 1/4-28 NF. Threads will be every bit as strong as the original part. I did that with a 1955 Elto 22.5 HP, worked just fine.

Hope this helps.

Best,
T2