Master link.
Hi, BlkAngusMan.
In SALT tracks (Sealed And Lubricated Track), each pin has a tapered hole in the end with a plug sealing the oil inside the pin. These tracks usually have bolt-up master links. These master links can be identified by the serrated joint running diagonally from the rail running face to the track shoe face of the link. Removing the four bolts holding the track shoe in place will break the link.
In earlier, non-SALT track, the master pin is an interference fit in the master link and must be driven in and driven out. These master pins usually have a tapered depression in one or both ends to identify them. You may have to check the inside ends of the pins if someone has put a one-ended master pin in back to front, with the ID mark on the inside. If the track has rock guards running full length along the bottom, you may have to move the tractor to find the master pin or link if it happens to be on the bottom when you start.
With the master pins, you need either a track pin press or a good heating torch, a large hammer and somebody with a strong back - and maybe a weak mind too - to swing said hammer. You will also need a GOOD drift with a good handle to drive the pin through the link.
A good freezer close to the work area or some dry ice will help in getting the master pin back in. Freeze the pin well beforehand and only take it from the freezer or the dry ice when you are completely ready to drive it back in. Be quick about it when you do.
Happy track-working.