Stock question

[Logangrimnar]

I recently purchased (haven't picked up yet) a c96 with a stock. The stock has a wheel at the front of it that locks it to the grip. I have looked at bunches on line and can't find another example of this. Can anyone tell me an information on this? Approximate age? Is it correct for a c96? Why is it different than every other one I've seen that just slides into the grip? Thank you in advance