noob question about pistons from silencerco

[maxmayhem]

These were opened when I bought them. So the packages are wrong I just figured out posting this question. Well, that being discovered, I have a piston labeled 14mm LH and another labeled .5 x 28. Two dumb questions--what is the intended use of the 14mm piston? I am assuming that .5 x 28 and 1/2 x 28 are the same though there is a distinction in the two baggies with one being labeled extended. Will the piston labeled .5 x 28 work for glock 17, a vp 9 and a cz p-07. What do I need for a cz scorpion which I was told would work for the scorpion (errantly). This is a little confusing since I dont have my suppressors so a little help is appreciated and some explanations.

Also, what piston would I need for a sig p250 and a sig 938?

I should also add that I have a silencerco hybrid and a silencerco octane 9mm in jail.

[chase]

The 14.5mmX1LH piston is for HK .40S&W pistols like the USP40 Tactical. I have one of those and a threaded barrel for my P2000SK.

Not sure about the two 1/2"X28 pistons if they are the same length. I figure one should be longer than the other.

[Fulliautomatix]

Depending on your CZ Scorpion's year of manufacture, you could possibly need a 18x1RH adapter or 1/2"-28. You seem to have already ruled out the 1/2"-28 threads, so go for the 18x1RH.

http://cz-usa.com/product/cz-scorpion-e ... -pistol-2/

2016 model year SKUs (91351/01351 and 91352/01352) feature 1/2×28 threads hidden underneath the factory flash-hider, meaning users can fit either 1/2×28 or 18×1 accessories to the muzzle.

I'm pretty sure early models are all threaded 18x1RH, so ideally you'll want a 18x1RH threaded fixed mount for your Octane.(Since the Scorpion is a fixed barrel blowback operated) SilencerCo part number AC1348

Your Sig P250, if a factory threaded barrel, will need a 13.5x1 LH Piston, again, SiCo offers standard and extended length, not sure which the P250 would need.
HK VP9 factory threaded barrels are also 13.5x1LH
Standard is AC26
XL is AC626

Sig P938 factory threaded barrels are 1/2"-28RH
Glock 17 factory threaded barrels are also 1/2"-28RH
CZ P-01 factory threaded barrels are also 1/2"-28RH
Standard Length - AC25
XL Length - AC59

So it looks like you'll need/want 3 devices to make your suppressors work on all your pistols listed above.
18x1RH fixed mount for the Scorpion
1/2"-28RH piston for the Glock 17, CZ P-01, P938
13.5x1LH piston for the P250 and VP9

[Joshua@CapitolArmory]

Sig, HK, Glock (EU guns) are metric from the factory.
American guns (and aftermarket barrels made in america) are usually standard. There's some exceptions, like P220 and FNX are .578 instead of m16, and MK23s want to be a special snowflake.

Generally speaking,

1/2x28 is domestic 9mm
13.5LH is European 9mm

9/16 is domestic 40
M14 is European 40

.578 is domestic 45
M16 LH is European 45, M16RH is MK23.

The extended or XL pistons are to allow a suppressor to clear a guide rod, or in the case of the Osprey and MPX, to extend the suppressor out to get past the hand guard.

Older CZ Scorpions (2015 versions) are Metric 18, so you need the M18 fixed barrel mount for an Octane.
New CZ's (new ones from the later half of 2016) are M18 and 1/2x28, so you can use either.