I need help with a target rear sight

[FlightRN]

Good Day All,
In my recent move from the UK back to the US, I lost the ejector screw that goes to my John Wilkes target rear sight for the No4 Mk1 rifle. Can someone PLEASE let me know what the thread diameter and pitch is for this screw. My brother-in-law has access to the equipement and can make it for me if I can give him the dimensions.

Thank you and Merry Christmas!

Michael

Information

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[tbonesmith]

The ejector screw is 3BA, so if the sight uses that hole to mount to, 3BA would be the go.

[RJW NZ]

If you're talking about the screw that goes into the left side of a No4 receiver to eject the shells, and if a Wilkes sight is held on with that screw the same way parker hale PH5c's are held, then the answer is to get the eject screw that is made slightly longer so it will mount the sight and still have enough length to engage the shell. They are available in several places, although perhaps you're keen to make one up for the fun of it.
The longer eject screw, made to mount a PH5c and similar aperture sights are often for sale at EFD.com, plus Evans Screws (listed on enfield resource.com in the alphabetical section), they are also pretty always for sale on ebay from oiler mark and other enfield enthusiast sellerss, there's a listing at enfield resource.com for ebay sellers too.

[jona]

If your brother has access to the Machinists handbook, have him look up British 3BA. All the dimensions will be there. If not let me know and I will dig out my copy, though it may take awhile.

[Patrick Chadwick]

Please note - BA screws were derived from Swiss watchmakers screws, which is why the spec. goes down to 25 BA! (never seen one, but I do have down to 16BA for modelmaking) and are specified in METRIC dimensions.
I have added 8-36 dimensions, as this is a possible emergency-fix option!

BA No. 3 OD 4.1mm (exact) = 0.1614" (approx) 8-36 = 0.164"
Pitch 0.73 mm (exact) = 34.84 tpi (approx) 8-36 = 36 tpi
Core dia. 3.22 mm = 0.127" 8-36 = 0.130"
BA threads have 47.5 degrees included angle 8-36 = 60 degrees

If you are desparate, then a mild steel 8-36 screw could probably be eased in, as the length of thread is quite short - if you first turn off about 4 thou from the diameter and then repeatedly screw in/out/in/out until the screw thread has adapted to the thread in the (harder) receiver. I use a kind of aluminium foam anti-siezing paste for this kind of work.


Patrick

[Patrick Chadwick]

BTW, I forgot the obvious possibility (why look for a simple answer, when a complicated one will do?) which is common-or-garden metric 4mm x 0.75 pitch.


Patrick