Drilling Subs Types & Applications
Subs are short pieces of tubular material used to increase the versatility of the main component of the drilling string. The simplest is a crossover sub, which connects two items with different threads. Others used in the drill string are:

- float sub

- dart sub

- circulating sub

- bent sub

- Bit sub

- Orientating sub

- Totco ring

- Side entry sub

- Bumper sub (Check the previous article)

- Shock sub (Check
https://www.drillingmanual.com/drilling-subs/