this type of drill collar is made of 4145H or 4145H modified alloy steel and has spiral grooves on the pipe body of drill collar. this will decrease the surface area contacted with the hole of the oil well, which will greatly reduces the probability of pressure differential detention occurring. 

 

 

Grooved Drill Collar

OD Range (in)	4-4 3/8	4 1/2-5 1/8	5 1/4-6 3/8	6 1/2-7	7 1/8-7 7/8	8-8 7/8	9-9 7/8
Depth of cut (in)	6 2/3 ± 1/32	7/32 ± 1/32	1/4 ± 1/32	5/16 ± 1/16	11/32 ± 1/16	3/8 ± 1/16	13/32 ± 3/32
Spiral Pitch (in)	36 ± 1	38 ± 1	42 ± 1	42 ± 1	64 ± 1	68 ± 1	72 ± 1