Sub Cross-over pin*pin 

Sub Cross-over box*box  

Crossover sub is mainly used to connect upper and lower drill tools in different connectors in drilling operations. Also it can be used to protect other tooling in drill stem (called saver sub) or be used to deliver outgoing air to the bit face just above the bit (called bit sub).
The length of crossover subs is generally measured from shoulder to shoulder. Typical lengths range from 6" - 28" long going up in increments of 2 inches with AISI 4145H, AISI 4145H Mod, AISI 4340, AISI 4140-4142 and Non-magnetic material. All connections are phosphate-coated or copper plated to improve resistance to corrosion. Crossover subs come in three basic types: A Pin (male) * Box (female); B Pin (male) * Pin (male); C Box (female) * Box (female)