1/2 - 20 threading

1/2" is pretty skinny for a .30 cal. I've done them, just not a fan- and that's 1/2"-28.
1/2"-20 is awfully coarse... will remove another .017 or so from the barrel wall thickness, doesn't sound like much but I'd keep all I could.
I've never seen a 1/2"-20t brake...

JMOYMMV

1/2-20 is prob a typo. They’re both prob 1/2-28.

Rubicon Precision said:

1/2-20 is prob a typo. They’re both prob 1/2-28.

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This

Some people do non standard gun threads so there isn't a blow up if someone puts a can on it. Agreed 1/2-20 leaves walls too thin. Might not be too bad just for a muzzle brake.

Read about here.

1/2 20 pops up on airguns a lot that I've seen, but haven't seen many mainstream firearms here with that going on.

1/2"X20 thread is standard US UNF thread.
Taps and dies available everywhere...as the standard fine thread for 1/2".
The 1/2" X 28 is not, but used in certain industries like the gun industry for muzzle breaks, where it's common there.
If it's not a typo, as there is no reason to change threads between these two steels...
Then go ahead and use a bushing easily made on a lathe, or buy, 1/2"X 20 to 5/8"X24...then install a standard 30 cal brake 5/8"X24.
Or just machine a muzzle brake to fit... with 1/2"X20 thread.

For those who don't know thread depth, or have a machinery hand book.

So let's correct the miss information.
1/2" X 20 is a standard USA die for 1/2" fine tread, I have one purchased at the local hardware store.
The 1/2" X 28 is special order, extra fine thread...not common ...only common in firearms muzzle break threads.

Next this is exactly what a 1/2" X 20 looks like on a .308" bore.
Not my choice but enough metal with low muzzle pressure not to be a problem at all.

Next is a factory manufacturered barrel with a 1/2" X 28 thread on a 9mm compared to 1/2" X 20 .308" I just made for comparison. Whoa! Talk about a thin wall!..threads and all!

Next is with the 1/2 X 20 .308" barrel threads turned off ...there is still plenty of metal support, for .308" bore.

Rubicon Precision said:

1/2-20 is prob a typo. They’re both prob 1/2-28.

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1/2-20 is very common in europe.
Both my CZ 457's (Canadian imports) have 1/2-20 threading but those are .22LR.

Thump_rrr said:

1/2-20 is very common in europe.
Both my CZ 457's (Canadian imports) have 1/2-20 threading but those are .22LR.

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Metric is probably common in Europe, for most rifles designated for use in European countries. Imports can change that.
1/2"X 20....IS "the standard" for the USA fine thread by the SAE!.... Period...
1/2" X 28 is the odd ball!...not in common use like the 1/2"X 20 thread, found on most hardware stores in the USA.
You have to special order taps and dies that are extra fine...like the 1/2" X 28... from Brownells, tooling outlets like Graingers, or somewhere that sells gun parts...cause that is one of the few places 1/2"X28 is common...is in muzzle devices for firearms...it's not in common use anywhere compared to the SAE coarse and fine threads in use.
The metric similar would be 14 mm X 1.5 mm for their common fine thread designation.
But they could make a non standard extra fine of 14 X 1 mm if they want, for the commy/ European muzzle breaks...it's up to the manufacturer.

My 8.6 Blackout has 18 mm X1.5 mm "the standard" metric fine. You can find a tap at the local hardware store...bore out the 5/8" X 24 and retap with 18 X1.5 mm to fit any American muzzle brake with that thread, to the metric barrel thread, as long as the .338 bullet has clearence... or bore it out too.
Simple, but many whine about the thread size and being metric.