Of bike frames! Get your mind out of the gutter already.
Anyway, rear ends, or rear forks, or as most people call them- dropouts. The dropouts are key to completing the whole look of a frame- especially on a fixed gear bike. Way too often you see a great custom frame ruined with cheesy premade drops that don't match the angles of the frame. This isn't to say there aren't some pretty nice drops out there, but if you want it done right.....
Towards that end, here's where Israel's drops begin- in a sheet of 3/16" 4130 steel. Much stronger than the 1010 steel most drops are made from. Three hourse of grinding, drilling, and filing nets us these (this is usually where I cut myself and today was no exception- a little blood in every frame, free of charge!)
How it looks about 30 seconds after the torch is shut off. I leave the seatstay tab a little wide so it can be shaped to the perfect angle later.