Mauser M12

[Lawdog]

I acquired a Mauser m12 and it does not have a cap on the threaded barrel. Can someone please tell me what size threads this gun is and if it’s right or left hand threads?
I bought a 15m x 1 RH cap and it will not thread on.
Thank you.

 

[AimSmall]

15mx1 per Mauser website.

A caliper and thread gauge would help.