I agree with Chuck, you have to do a few hard hits or else it will flatten the top. The first one went in fairly easily for me, but you have to bend it back with a pair of pliers so it stays straight. The second time, I didn't bend it back and it went in way crooked. I ended up breaking off the bent and mangled mess, and after that there was only 1 or 2 mm left on each side, which happened to be enough to hold the gear on.