1/2 - 28 9mm

Your barrel will have had to have been threaded ( 1/2-28 TPI ) to be able to attach this unit.... 13.5mm left hand threading is also avaliable....

SPECIFICATIONS:

Machined from : 6061-T6 Aluminum
Thru Hole 10.5mm for 9mm
Length 5"
Threads: 1/2'' - 28 threads per inch. 
Diameter of body: 1"
Thread depth: 1/4"
Finish: " Flat Black" 

God Bless the U.S.A.

Thanks for Looking !!!!!!