PH Aperture thread size

[series2a]

Anyone know what thread size the Aperture sight is? Ie main 6 hole sight that screws into the swinging body.
BSF I would imagine?

[Troubledshooter]

Unfortunately, I can't find the thread diameter in the Parker Hale catalogue 62, although they do give the diameters of all the different eyepieces available.

[series2a]

Am I right in thinking it’s got a slight taper on the eyepiece ?

[bill57]

7/32 x 40. Think the American makers (Lyman, Redfield etc) are the same dimensions BUT the thread form is a different shape, so they're not interchangable. They will screw in a bit, then bind, which is maybe why it seems like a taper?

[MDriskill]

7/32 x 40. Think the American makers (Lyman, Redfield etc) are the same dimensions BUT the thread form is a different shape, so they're not interchangable. They will screw in a bit, then bind, which is maybe why it seems like a taper?

Correct. The American sights use a standard US 60-degree thread angle, where the British one is a Whitworth thread (? - one for you machinists out there) that is more like 55 degrees. This makes the screw slightly larger in overall diameter.

That being said, if my memory is correct, PH eyepieces will usually fit in Lyman sights, but not Williams (have never tried a Redfield). US eyepieces will fit easily in PH sights.