Abstract: Multi-stage ball bearing assembly mounted internally of a floating plug or the forward end of a mandrel and including a plurality of axially aligned ball bearings for enabling rotation of a spinner for forming at least two internal spiral grooves in the inner portion of tubing upon relative motion therebetween to produce at least one spiral fin internally of the tubing. The ball bearings include inner and outer ball tracks and a plurality of spherical balls which roll between the tracks. Predetermined ones of the outer ball tracks are displaced axially with respect to the inner ball tracks in the same direction as the relative movement between the tubing and the spinner to provide relief space in the direction of relative movement which, upon rotation being imparted to the spinner which in turn imparts rotation load to the multi-stage ball bearing assembly in the same direction of such relative movement, causes the rotation load to be distributed substantially equally between the ball bearings.

Abstract: Process of providing the internal portion of tubing with at least one spiral fin, comprising the steps of: providing a first spinner having at least two first external spiral ridges displaced a predetermined distance angularly with respect to each other and providing a first spiral groove therebetween having a first depth and providing a first spiral path; producing relative motion between the first spinner and the tubing internal portion to cause the first external spiral ridges to engage the tubing internal portion and form spiral grooves therein and to cause a portion of the tubing internal portion to flow into the first spiral groove and form a spiral fin; providing a second spinner having at least two second external spiral ridges displaced the predetermined distance angularly with respect to each other and providing a second spiral groove therebetween having a second depth greater than the first depth and providing a second spiral path; and aligning the second external spiral ridges of the second spinne