WARNING!!! Do you have one of these?
If you have one of these mechanics seats, you need to inspect it to see if it is built like the one in the first pic. The metal frame is made in 3 parts. The front part is connected to the two curved up rights (where the seat mounts)with two plastic square bars that are pressed in to the square tubing and held in place with a screw on the bottom and a roll pin on top. These things will brake and when they do they will dump you backwards on to the floor . Can result in some very serious injury. It happened to me , it dumped me backwards on to a concrete floor, I was lucky my head hit the pillow part of a creeper that was behind me part of the plastic tray came up under my arm pit and took the hide off from my elbow to my arm pit. At my age I don't bounce real good any more.
To fix this so it could not hurt my or any one else I butt welded the frames together and capped one side and the bottom with some 1/8 th inch flat strap.
After this happened I found out other people had the same problem with this seats. So if you own one or use one at work ,check the thing out and fix it so you don't get hurt.