In case anyone needs a little help......I would like to give credit to Coils for bringing this tutorial to our attention
Underfolder Assembly Instructions
1. Position folder onto the receiver
2. Slide the sling swivel (5) onto the center support pin (3).
Put locking lug (6) in the receiver with it's lugs pointing to the left side of the receiver so the center pin will slide through it. From the left, slide the center pin through the folder making sure it also slides through the locking lug.
3. Slide the locking nut (7) onto the shaft of the external locking lug (8). Then slide the shaft of the locking lug into the right side of the center support pin.
4. Insert one of the pins (4), through the center support making sure it is also going through the slot on the shaft of the external lug. Try all three pins until you find the one that fits best. You want an equal amount of pin sticking out each side.
5. Grab the sling swivel and turn and push the center support until the pin you just installed slides into the cut outs in the trunion. This pin keeps the whole locking assembly from rotating.
6. Screw the locking nut onto the threads of the center support until it fits snug. Not too tight, not too loose.
7. Once snug drive one of the other pins (4) through the nut. This has to be in a vertical position so it will line up with the hole in the center support and the slot in the shaft of the locking lug.
8. Push both locking lugs so their tabs are snug with the trunion locking holes. The folder should now be locked in the open position.
9. Insert the push button spring (2) into the left side of the center support.
10. Insert the push button (1) into the left side of the center support. You should feel the spring compress. Make sure the holes are in the vertical position.
11. Push in on the push button until it's holes line up with each hole in the locking lugs. Insert the last pin (4).
12. Tap it down flush with the locking lug. In order to remove this pin you will have to drill a hole in the bottom of the receiver. Not to worry, because it will be covered up by the pistol grip. Your folder is now assembled.