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I need some help on determining what thread size these two barrels have. They are the same size. One is a nosler m48 sporter barrel and the other is a sako a7. I need to get an adaptor to size them up to 5\8 x 24. I have a suppressor on the way. I have searched manuals to no avail. I found one suggestion its 1\2 x 28. Thanks for any help

Buy or borrow a thread pitch gauge. They are relatively inexpensive and handy to have around.

drover

You are certain they're the same? It'd be very common to have 1/2-28 or 5/8-24 on the US made rifle but a quick search shows some A7s to have 15-1 metric thread? Just measure the od of the Nosler threads and you'll know fairly certain if it's the common 1/2 or 5/8. 1/2-28 to 5/8 -24 adapters are readily available ranging from sloppy junk to nicely machined. A guy was selling very nice ones in the Classifieds here.

They are the same. The thread protector cap fits both rifles. I will try and find the add. Thanks

You might measure before buying. Hard to tell from here. LOL

Take the thread protector to the hardware store. Most likely they have a gauge by the nuts and bolts.

Likely the action screw on the Nosler is 1/4-28. Remove an action screw and lay the threads up along the muzzle threads. You’ll know immediately if the threads are 28 pitch or not. A ruler will tell you if the thread is 1/2” in diameter.