The stock pin is nothing more than a metallic cylinder that rests in the middle of the hinge mechanism of the stock. In rifles such as the G36C, you may want to fold the stock whenever you enter a building. This way you have better maneuverability in enclosed spaces. Mostly, what you want is the ability to quickly change hands depending on how you are going to enter a door. Outdoors, the stock should be unfolded so as to let the shoulder absorb recoil (but we’re talking about airsoft here, so nobody’s gonna complain if you don’t).
My G36C replica has been giving me some problems whenever I fold and unfold the stock. Which is pretty much always, since I keep going in and out of buildings in my usual fields. The stock pin keeps falling off. No big deal, since it never falls completely, but still an inconvenience.
I may not have a lathe to make a replacement with a slightly bigger diameter, but a 3D printer is equally useful in this case. Moreover, I’ve seen G36C’s from other makers which have pins with a different design that prevents falling, so I guessed I could add something like that.
Stock pin 3D model download
After some tinkering with the right diameter, I settled with this design:
Download G36C Stock Pin STL
When you print it, make sure to lay the design as in the picture. One of the sides of the cylinder is actually a little bit flat so that it adheres better to the print surface. Plus, if you printed it vertically the layer adhesion would be so weak that it would break the first time you pull it out of the hinge.
Notice that there is no chamfer on the lower end to insert the pin more easily. At first it will be tight to insert, but afterwards the plastic on the end face will have deformed a little and this will help in making the pin difficult to extract accidentally.