Finally getting back to a 32-20 Low Wall. Finish is pretty beat, but bore is good, action is tight... Trying to mount a Marble Flexible Tang Sight [W1 base] on it -AND- use the correct screws. 

IMHO, don't waste your time searching for the correct Marble Screw Set on Midway. The compatibility guide is a scream, the individual screw set pages usually don't have the screw size, and I felt darned confused.

Point your browser to Buffalo Arms, each set is illustrated with an actual picture of the screws -AND- they list the size / thread / length. I ordered two different sets.

I've contacted Marbles for the correct screw sizes for an original 1885 Low Wall and was told 10-36 x .342 and 12-28 x 2.235.... Referring to the book "The Winchester Single-Shot", Volumes I and II, the upper tang screw is called out as a 12-28, but the Sear Spring Screw is called out in Vol I as a 10-32, while in Vol II it is called out as a 10-36. On this Low Wall, the sear spring screw is a 10-32 [Brownell Screw Checker], but it is possible the original threads were trashed and a 10-32 tap was used to chase the threads. The threads aren't smooth, but I am not going to try recutting them...

The 12-28 x 2.235 length didn't make sense on my straight stocked Low Wall [1.650 OAL w/o sight] Further reading suggests it might be correct for a pistol grip rifle.

In Vol II, page 193 has a table [from ASSRA!] that has the mounting screws for the Flex sight. Of course, the current Marble's tang sight screw table uses current threads [no 35 1/2 tpi]. The date of the table appears to be either 1919 or 1920.

Where is this period Marble Tang Sight screw table? It shows the head diameter and suggests the screw heads have straight sides, not angled.

PS. Correct and lucid spelling is fun!

A tang screw slot that's 7/32" = 0.21875" wide)?

Bill Lawrence