The Box Tap is constructed of high-grade steel, with tool joint connection in the top, and then heat-treated.
The Die Collar is constructed in the same way except it has casing or washpipe connection in the top.
The Box Tap is used where the exact size of the fish is not known, or sometimes to catch two or more fish at one time.
The Die Collar is used primarily to tie two strings of pipe together, such as tubing or casing, or where a large I.D. is needed.
These tools are not designed to be released. Sometimes you can jar on them or work them up and down, then put left torque in the pipe and screw them off the fish. EXTREME CARE SHOULD ALWAYS BE USED WHEN PUTTING LEFT TORQUE IN THE PIPE.
After pulling or jarring on either for a short time it is a good idea to set the string weight at a neutral weight and tighten them again.