Help wanted.

Would anyone in the group know what size and thread screw was used to fasten the fibre base on an RCA 100A speaker?

Mine is missing the screws and in repainting the speaker I managed to dribble some paint into the holes, although I am fairly sure I can clean them out.

This leads to.. where can I get hold of the right screws in this metric age.

Harold

It'd be best if you sent me a photo of where the screws go on the speaker for publication. There were several types of imperial threads, Whitworth, UNC, UNF, etc. Being American it's more likely to be one of the latter two though it also depends on whether the screws are self-tapping or have machine threads.

Just clarifying, the screws are machine thread, not self tappers and photos are on their way. They would be about 1/2 inch in the old scale.

Probably 1/2 long but the gauge would be closer to 1/8 or 3/16.

Based on my repairs of American equipment that is likely to not have 1/8" or 3/16"

Before 1/4" the American system goes in Guages and neither the diameter, pitch, or thread angle are the same as Whitworth ( UNF: Same angle as metric)

The thread will be equivalent to Unified which was used on cars from 1950.

If all else fails a "bottoming" thread tap should clear the hole. There are various suppliers Engineering, Automotive & Hobby that are liable to have them as a stock item.

Marc

Thanks to all for your suggestions, I am sure they are UNF as Google tells me that they have been in use for ever.

My problem has been resolved as I remembered I had an old US chassis, rusted beyond any hope of restoration, and sure enough, it used the right size screw for the valve sockets. I had to shorten them to the correct length and the residual paint was not a problem, the right screw went in quite easily.

Harold