Definition - What does Spider Sub mean?
A spider sub is a mechanical component that attaches to a drill pipe. The purpose of this component is to hold the pipe in position and prevent it from sliding through the rotary table and into the well. A spider sub must be designed such that it can hold the weight of the entire drill string, which is connected below the rotary table.
Trenchlesspedia explains Spider Sub
A spider sub is specifically used in those applications where the bushing size of the rotary table does not match the size of the piping. The spider thus does not fit in the table hole but rather rests on the table surface. Spider subs grip onto the body of the pipe directly and not onto a collar, so they can also be used in applications where collarless piping is used. The immense pressures exerted on a spider due to the weight of the drill string and the torque of the rotary table require regular inspections for degradation or potential failure.