Letterplate screws

[JohnD]

I need some slightly longer ones. What size are they likely to be? They look like 6mm but are not a metric thread The plate is some years old but not an antique.

 

[cmother1]

On older door furniture you commonly find 3/16" and 1/4" Whitworth threads (BSW). A 1/4" thread will have 20 pitches to an inch - coarser than the nearest metric equivalent (6mm).

Allscrews in King St, Hammersmith used to do Whitworth studding, but I haven't used them for decades.

If you can get hold of a die nut the right size you could cut the head off a long metric coach bolt and put a Whitworth thread on the sawn off end. This isn't a precision engineering job, but it's good enough for what you want to do.

 

[JohnD]

thanks, I will see if I can lay my hands on a 1/4" Whit and try it for fit

 

[JohnD]

you were right, cmother1. I couldn't find any in the garage so I ordered a few 2" x 1/4" BSW and they are the right one for the job. I tried them in several letterboxes and they fit all of them, so I suppose it must be standard.