RHPBSB078QULP4Ball Screw Support Bearing 20x47x16 mm, Thrust Angular Contact Type, P4 / ABEC 7, Universally Ground for Preloaded Multi-Bearing Mounting

Product Description

What this part is

An RHP BSB series ball screw support bearing, 20 mm bore, 47 mm outside diameter, 16 mm width. The BSB family is a purpose designed thrust angular contact bearing for the fixed end of a ball screw, ground for universal mounting so that two, three or four bearings can be clamped together to build the required preload and stiffness.

Decoding the designation

BSB — RHP Ball Screw Bearing series.
078 — the size code within the series, corresponding to the 20 x 47 x 16 mm envelope.
QUL — universally ground with light preload, in the multiple bearing set form the series is built around.
P4 — ABEC 7 tolerance class.

Why this is not an ordinary angular contact bearing:
This is the single most important thing to understand about the part. A 20 x 47 x 16 mm envelope looks close to a general purpose angular contact bearing, and it is not one. Ball screw support bearings use a much steeper contact angle than a standard 15° or 25° spindle bearing, precisely because a ball screw end sees almost pure thrust and almost no radial load. That steep angle buys very high axial stiffness and axial load capacity, and it deliberately sacrifices radial capacity and speed. Substituting a standard 7204 class bearing into a ball screw end is a classic and expensive mistake: the machine loses positioning stiffness, backlash appears under reversing load, and the bearing sees a thrust load it was never rated for. The reverse substitution is just as wrong. We are not publishing a numeric contact angle for this part because RHP’s figure for the BSB078 is not something we could verify from the manufacturer, and this is a specification where a guess would cause real damage.

Quantity and configuration

BSB bearings are supplied and used as universally ground units that are clamped in multiples to set preload. Our stock is held in a way that does not distinguish sets from individual pieces, so no set count is claimed here — tell us the arrangement you need and we will confirm what is physically on the shelf before you order.

Fitting notes

Clamp both rings solidly against square, ground abutment faces; a ball screw end bearing that is not squarely seated transfers its misalignment straight into screw runout and shortens nut life. Preload comes from the ground ring offsets when the stack is clamped, so the clamp nut torque matters. Observe the marked ring orientation.

Published ratings and mounting data

Contact angle, dynamic and static load ratings and limiting speed are not published for this designation in any manufacturer source we could verify, and they are left blank rather than taken from a nominally equivalent part in another brand’s catalogue.

Interchange guidance

Obsolescence trail: RHP to NSK. The 20TAC47 reference carried in the title is the NSK ball screw support form for this envelope (TAC being NSK’s thrust angular contact code), and BSB078QFEP7 is an RHP variant in the same size with a different grade and preload code. Both are retained as search terms. The title’s MM9306 WI 2 DUH string from the old source data is a Fafnir style number for a standard spindle bearing rather than a ball screw support bearing; it is retained as a search term only and should not be treated as an equivalent.