I got this used, and can't find anything about it. My 45 MOS Threaded Barrel doesn't have this red rubber band looking thing. Attached File

An O Ring?

To keep the thread protector from coming loose.

Thanks! Is it definitely necessary? Wondering if I need them for my other threaded barrels.

It probably wouldn’t hurt anything to have them on there

Not necessary.

Some thread protectors seem to stay in place on their own.  Some tend to work loose and start to move a thread or more.

I guess if you remember to keep an eye on them during a shooting session and tighten as needed if they work loose then it's no big deal.  But, forget, and loose that threat protector in the dirt, grass, rusty steel brass out in front of the firing line and you might not find it.

I keep an o-ring on all mine just to make sure I don't loose one.

I just went to Lowes, bought one of the little plastic containers of different sizes and then looked through them till I found the right size and then bought a box of the right size.  Can't remember which size that was now and I need to buy some more, just to have when one splits/cracks and needs to be replaced.

The red looking o-ring is likely silicone rubber which has a much higher temperature rating than the hardware store black nitrile o-rings. 500 F vs 225 F.

I would leave the ring in place. it helps keep the thread protector or other muzzle device tight without having to use thread locker.

Some companies mill a notch and some don't.  I prefer those that do.

As pointed out, it's an o-ring.  The metric threading Glock uses for their barrels is a bit coarse and the o-ring helps to retain whatever is screwed on.

In my experience Glock OEM barrels used without o-rings invariably loosen; OEM barrels used WITH o-rings stay nice and snug.

also take it off before you attach a can.

Be sure to check your thread protector every 50 rounds or so.  Even with the o-ring it’ll loosen up quickly.  I’ve had them fall off before.

Anyone know what the proper o-ring is?

ETA:  upon further research

hhttps://www.amazon.com/dp/B005RUPI00/ref=cm_sw_r_cp_api_glt_fabc_GGCR23KZX7YS55YHXQRK

Viton