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API Standards For Rock Bits And PDC Bits

API standards, as established by the American Petroleum Institute, enable drilling professionals the world over to communicate clearly.he American Petroleum Institute:
*maintains more than 500 standards and recommended practices
*represents the oil and gas industry to the public, Congress, state governments, and media.
American Petroleum Institute Standards for PDC and Rock Bit Tolerances
Bit Size (In.) O.D. Tolerance (In.)
6 3/4" and smaller -0.015 to +0.00 PDC -0.0 to +1/32 Rock Bit
6 25/32" to 9" -0.020 to +0.00 PDC -0.0 to +1/32 Rock Bit
9 1/32" to 13 3/4" -0.030 to +0.00 PDC -0.0 to +1/32 Rock Bit
13 25/32" to 17 1/2" -0.045 to +0.00 PDC -0.0 to +1/16 Rock Bit
17 17/32" and larger -0.063 to +0.00 PDC -0.0 to +3/32 Rock Bit
PDC bits are gauged by either a "go" gauge or a "no go" gauge.
A "no go"gauge is used to ensure a bit is not smaller than allowed and, as the name implies, it should not go or slip down the entire length of the bit.  A "go gauge ensures a bit is not larger than allowed and should slip down the entire bit.
Rock Bit Size and API Standard Connection
3 1/2" to 4 1/2" drill bits - 2 3/8" API Reg. pin
4 5/8" to 5 1/2" drill bits - 2 7/8" API Reg. pin
5 5/8" to 6 3/4" drill bits - 3 1/2" API Reg.pin

7 1/2" to 8 3/4" drill bits - 4 1/2" API Reg. pin  
9 1/2 " to 13 3/4" drill bits - 6 5/8" API Reg. pin                  
14 3/4 " to 26" drill bits - 7 5/8" API Reg. pin