NSK44TAC76ADFFBall Screw Support Bearing Matched Set 44×76 mm Face-to-Face Arrangement 4 Pcs

Product Description

What this part is

A factory-matched set of ball screw support bearings from NSK’s TAC series: thrust-biased angular contact ball bearings built specifically to locate the end of a ball screw. Bore 44 mm, outside diameter 76 mm, supplied as four pieces ground as a 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 44TAC76 reads directly as 44 mm bore in a 76 mm outside diameter. TAC identifies the ball screw support family, A the internal design series, and DFF a factory-matched multiple-bearing arrangement in the face-to-face family. This convention is distinct from the ISO 70xx and 72xx 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 equivalent 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 bore and outside diameter match.

What a matched multiple set buys

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 appears directly as lost motion in the axis. Stacking several bearings raises the axial stiffness and the thrust capacity roughly in proportion to the number of rows sharing the load, which is why heavily loaded or long screws use three- and four-bearing stacks rather than a single opposed pair. Grinding the pieces as a factory-matched set is what makes the load share evenly: the ring faces are relieved to matched heights so clamping the stack solid develops the intended preload across every row at once.

A face-to-face oriented stack converges the load lines rather than diverging them, which makes the arrangement more tolerant of angular misalignment between the screw journal and its housing than a back-to-back stack of the same size.

Quantity and configuration

4 Pcs, supplied as one factory-matched set.

Fitting notes

The stack seats in the screw’s support housing with the thrust faces oriented as the face marks indicate, and the pieces are kept in their supplied order and orientation because the matched grind belongs to the set as a whole. The locknut on the screw journal is drawn up against the inner ring face so clamping load passes through the rings and never through the ball complement. Seats at this tolerance class are ground and measured.

Interchange guidance

The full designation 44TAC76ADFF is the identifier to match, and the arrangement code is part of it. Related sizes rather than interchanges: other bore and outside diameter combinations in the TAC series, other tolerance classes, and the DB, DF, DBD and DFD arrangements of the same envelope, which are ground to different set stack heights and row counts. Ordinary angular contact bearings of the same envelope in the 70 or 72 series are a different family. Individual pieces separated from a matched set are not equivalent to set stock.