The locking block pin (ie: third pin) serves no purpose for 9mm. If you look at generation 1, 2 and early gen 3 9mm Glocks, they don't have the locking block pin (ie: known as "2 pin Glocks"). When Glock introduced pistols in .40 cal, the higher pressure of the .40 needed the locking block pin. As the G17/G19/G26 shared the same frames as the G22/23/27 Glock decided to make those frames with the 3rd pin to simplify production.

Note that current 5th generation Glocks, which are only 9mms, don't have the 3rd pin.

 

1998 and 1999 Glock 19s. They are 2-pin Glocks but you can see the indentations in the frames where the 3rd (locking block pin) would have gone if these frames were meant to be .40 cal. pistols.

 

As others have said, the third pin was added with the advent of the 40 cal. It was to keep cavitation of the locking block to a minimum with recoil of the 40.

At the time the long term effects of the higher recoil of the 40 having ill effects on the polymer, wasn't completely known. It was more of a preventative maintenance thing than it was a mandatory addition, because of failures.

Years later enough data has been provided by long term usage to determine the third pin really isn't needed. Yes the 9mm didn't need them, but Glock is also producing 40 caliber pistol in the 2 pin design now.

One of the MHS guns submitted, a 23X style pistol was a 2 pin gun. The Brazilian police just adopted a 5th Gen 40 caliber, also a 2 pin design.

I suspect there was a good deal of testing with those 40 caliber two pin guns. Any issues with not having the third pin would have likely popped up during their trials.

MHS23

Brazilian Gen5 40

I suspect we will see 40 caliber Gen5 guns before long. 40's are on the back burner right now, so Glock hasn't made it a priority to get them out.




TXPO

 

Don't those gen5 40s have the fat slide of the 37/38?

 

I remember reading in a post on another GT thread that Glock re-engineered the locking block for gen 5 pistols. I have no idea if the gen 5 locking block has been re-engineered, or after 2 decades of experience, Glock feels confident the locking blocks of old would safely handle .40 ammo without that 3rd pin.

In the past, in regards to the 3rd pin, I've always said "one more part, one more potential for failure." There used to be threads on a regular basis where a Glock owner would post they stripped the frame and, upon re-assembly and shooting the gun, the frame would go into slide lock after each shot. The culprit was usually due to incorrectly installing the slide stop lever vs. the 3rd pin.

Thankfully, I haven't seen those threads in a while!

 

Likely Glock experience will determine the future of that 3rd pin for future guns.
We as the consumers can only conjecture (second guess and talk) all we want about whether that 3rd pin locking block is needed, but they will have the actual numbers. It will save them money to eliminate it, if not (proven) needed.

Hopefully, they don't use "Boeing's" logic.

 

I have always wondered how much actual reinforcement the 3rd pin offers, since the amount of their bearing area in the frame is so small compared to the bearing area of the channels where the block fits.


Edit: Removed comment about pin hole elongation.

 

So I have everything for my 980 build besides the locking block will it go together without