E&M Specialty Co. in conjunction with South Louisiana Machine Shop can make any and all types of drill string subs. All subs made by South Louisiana Machine Shop are API inspected and certified, or they may be new with mill certs. Subs are shorter components of the the drill string, averaging only four feet in length. Most subs are used as an adapter between two different connection types in the same drill string. Often times the connection on drill pipe will differ from that of the bottom hole assembly (drill collars and heavy-weight) and a crossover sub must be used to adapt the two different connections. Another common type of sub is a bit sub. A bit sub is a sub that is used just above the bit and serves as a crossover between the drill collar connections and the bit connection, and it also houses the float valve. The float valve is basically a one way fluid valve that allows drilling fluids to pass out of the drill string and into the bit, but does not allow those fluids to back-flow into the drill string.