NSKBall Screw Support Bearing 38x72x16 mm Universally Ground Single High Precision

Product Description

What this part is

A ball screw support bearing from NSK’s TAC series: a thrust-biased angular contact ball bearing built specifically to locate the end of a ball screw. Bore 38 mm, outside diameter 72 mm, width 16 mm. It is universally ground, so pieces of the same designation stack directly against each other to form a preloaded set.

Decoding the order code

In this NSK scheme the leading number is the bore in millimetres and the number after TAC is the outside diameter, so 38TAC72 reads directly as 38 mm bore in a 72 mm outside diameter. TAC identifies the ball screw support family, A the internal design series, SU universal grinding, and PN7B the high-precision tolerance class in NSK’s ball screw support scheme. This is a numbering convention distinct from the ISO 70xx and 72xx angular contact series, where the last two digits encode the bore rather than stating it.

Ball screw support bearings as a family

These are a separate product family from ordinary angular contact bearings, and the distinction matters when qualifying a substitution. A ball screw takes almost all of its load axially, so a support bearing is built with a much steeper contact angle than a general-purpose spindle bearing, trading radial capacity away for axial capacity and axial stiffness. The comparable families are the RHP BSB series, FAG’s 7602 series, NTN’s BST series and Timken’s MM…BS series. An ordinary 70- or 72-series angular contact bearing of the same envelope is a different part and not a substitution, even where the bore and outside diameter match.

What these specs mean in practice

Axial stiffness at the screw end is what sets positioning accuracy on a machine axis. A screw located on a soft or unpreloaded support deflects under thrust, and that deflection shows up directly as lost motion in the axis. Preloading a matched pair or a stacked set of these bearings removes the axial play and fixes the screw’s position, which is why they are supplied universally ground for stacking. The high-precision tolerance class keeps ring runout low so the preload stays even around the race rather than varying with angular position.

Quantity and configuration

1 Pc. Universally ground single (SU), open on both faces.

Thrust direction

A single-row angular contact ball bearing carries thrust in one direction only. Thrust in the opposite direction is taken by a second bearing mounted in opposition, which is the normal arrangement at a ball screw’s fixed end.

Fitting notes

The bearing seats in the screw’s support housing with its thrust face toward the load, following the face marking. Universal grinding means pieces of the same designation clamp solid against one another to develop preload without shimming. Seats at this tolerance class are ground and measured, and the locknut on the screw journal is drawn up against the inner ring face so clamping load passes through the rings and not the ball complement.

Interchange guidance

The full designation 38TAC72ASUC11PN7B is the identifier to match. Related sizes rather than substitutions: other bore and outside diameter combinations in the TAC series, other tolerance classes, and the DB, DF and triplex factory-matched sets of the same envelope, which are ground to a specific set stack height. Ordinary angular contact bearings of the same envelope in the 70 or 72 series are a different family.