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1)used as lifting sub and safety slip when trip out, 2)as per API spec 7-1 .Hard banding is optional at customers request - details see: https://www.machineto.com/spiral-drill-collar-with-elevator-groove-and-slip-groove-10317609

The Spiral Drill Collar of Zhongzhong is made from AISI 4145H modified alloy steel, and completely meets the requirement of API Spec 7-1 and SY/T5144 Standard. It is a kind of drill collar which adds three dextrogyrate spiral groove on the outer circle of ordinary drill collar when processing, and the purpose is to reduce the area of contact and friction with the well wall, which can effectively prevent the pressure sticking. The single weight of the spiral drill collar is round about 4% lighter than the ordinary drill collar with the same specification, and the shape and thread of the both ends are the same with the drill collar.

Specification:

Connections	OD mm	ID mm	Length mm
NC23-31	79.4	31.8	9150
NC26-35	88.9	38.1	9150
NC31-41	104.8	50.8	9150 or 9450
NC35-47	120.7	50.8	915 or 9450
NC38-50	127.0	57.2	9150 or 9450
NC44-60	152.4	57.2	9150 or 9450
NC44-60	152.4	71.4	9150 or 9450
NC44-62	158.8	57.2	9150 or 9450
NC46-62	158.8	71.4	9150 or 9450
NC46-65	165.1	57.2	9150 or 9450
NC46-65	165.1	71.4	9150 or 9450
NC46-67	171.4	57.2	9150 or 9450
NC50-67	171.4	71.4	9150 or 9450
NC50-70	177.8	57.2	9150 or 9450
NC50-70	177.8	71.4	9150 or 9450
NC50-72	184.2	71.4	9150 or 9450
NC56-77	196.8	71.4	9150 or 9450
NC56-80	203.2	71.4	9150 or 9450
6 5/8REG	209.6	71.4	9150 or 9450
NC61-90	228.6	71.4	9150 or 9450
7 5/8REG	241.3	76.2	9150 or 9450
NC70-97	247.6	76.2	9150 or 9450
NC70-100	254.0	76.2	9150 or 9450
8 5/8REG	279.4	76.2	9150 or 9450