SW Guide scope mount

[TheThing]

I've recently acquired on of these SW Guide scope mounts but the hole sizes are driving me crazy!  There is a row of threaded holes (see pics)  down the centre, which would be perfect to attach my little guide scope to.  However, I can't fathom the size.  I tried M5 - too big, M4.5 - too big, M4 - too small.  Must be imperial so I've found some 3/16" - too small.  Now I've run out of bolts in my 'man draw' so before I look to purchase any, can someone help me with sizing please?  Be very much appreciated!

[Mandy D]

3 hours ago, TheThing said:

I've recently acquired on of these SW Guide scope mounts but the hole sizes are driving me crazy!  There is a row of threaded holes (see pics)  down the centre, which would be perfect to attach my little guide scope to.  However, I can't fathom the size.  I tried M5 - too big, M4.5 - too big, M4 - too small.  Must be imperial so I've found some 3/16" - too small.  Now I've run out of bolts in my 'man draw' so before I look to purchase any, can someone help me with sizing please?  Be very much appreciated!

M4.5 is too big, yet 3/16" is too small? 3/16" = 4.7625 mm!

Try 2BA = 4.70 mm

Also look at the pitch of the thread. 3/16" comes in UNC and UNF. Chances are that in aluminium, it will be a coarse thread (UNC?) and a 3/16" UNF will not just have the wrong pitch, but be too large on the root diameter.

[TheThing]

My bad M4.5 and M5 were too small, M6 and M7 too big. Getting confused with so many bolts on the table. Think a MM5.5 would be perfect but can't find them anywhere.

 

 

 

 

 

 

[Seelive]

2 hours ago, TheThing said:

... Think a MM5.5 would be perfect but can't find them anywhere ...

 

 

 

 

 

 

 

I'm not suprised, I've never come across one either!.  Usually SW threads are a standard metric sizes or they could at a push be American  UNC (or UNF). I very much doubt they would be Imperial BA, BSF or Whitworth (although a 1/4" Whitworth bolt will screw in a 1/4" UNC nut)