Little help please... grooved receiver/rail ring mounts.

[Ladobe]

Can't find my data or remember exactly how to measure...
 
Have a pair of ring mounts, no idea what brand.   I think that they are for 13mm grooved receiver or rail.   
 
Can somebody help me confirm please.
 
Thanks
 

[Lloyd Smale]

they look like 3/4 inch tasco 22 rings

Can't find my data or remember exactly how to measure...
 
Have a pair of ring mounts, no idea what brand.   I think that they are for 13mm grooved receiver or rail.   
 
Can somebody help me confirm please.
 
Thanks
 

[Graybeard]

Generally speaking there are two sizes 3/8" known as rimfire tipoff rings and 5/8" or Weaver standard.

If for a rimfire they are almost certainly the 3/8" tipoff rings. If for centerfire rifles then the standard weaver or 5/8" size. About the only way they would be a metric size is if they were made for some European rifle rarely imported into the US.

Over the years tube sizes of 1/2", 3/4", 7/8", 1", 26mm and now 30mm have been used. Almost all the smaller three I've seen only as 3/8" rimfire tipoff rings.

Thirteen mm is roughly a half inch and would be noticeably different than either the standard 3/8" or 5/8" that American rings come in.

[Ladobe]

Thanks for the input gentlemen, its appreciated.
 
Lloyd - these are not for a 3/4" scope, and they are not the same design/shape as any Tasco RM's I've been able to find pictures of current or vintage.
 
Bill - They are not either 3/8" or 5/8" - won't clamp down small enough for the first, will clamp on the second if I open them wide enough but puts the ring center off center from the base.   Why I assumed they are for a European firearm where RM's are in mm's - 11, 13, 16, 19, etc.   Then I measured for the scope tube and found that they ARE for a 26mm tube... yep, European which also means the clamp angle is different.   So these almost have to be 13mm, but I just wanted a way to measure to confirm.   They won't clamp down enough for 11mm; 16mm is close to our 5/8" so would offset the RM from he base.
 
Guess I have my answer just by deduction Sherlock... now I'll have to research to figure out who made them.
 
Now where did I put my Calabash pipe....