Plummer block, flanged or pressed steel housing

Short answer

Mounting surface parallel to the shaft — plummer block. Surface perpendicular to the shaft, a wall or an end plate the shaft passes through — flanged housing.

This is the one criterion you cannot work around: a flanged housing will not stand on a frame, and a plummer block will not bolt to a wall. Size, bearing fixing and housing material are chosen afterwards.

First the direction of the mounting surface, then everything else.

Plummer block housing

A body with a base, bolted to a horizontal or vertical plane running along the shaft. The manufacturer's catalogue holds 18 families — from split SNI, SN and SD to solid SIG, SIH and UCP.

Split versus solid matters at service time. In a split housing you lift the cap and change the bearing without moving the shaft; a solid one has to be slid off. On a long shaft with wheels or couplings already mounted, that is the difference between an hour and a whole day.

Split means service without removing the shaft. Solid means lower cost and less space.

Flanged housing

A body with a flange, bolted to a wall or plate perpendicular to the shaft axis — the shaft passes through the opening. This is the largest group in the catalogue: 34 families, among them FI, OI, RI, UCF, UCFC and UCFL.

Flanges differ in shape and bolt count: square with four, oval with two, round with three or four. The choice follows the space around the opening and the thread pattern — the housing itself works the same.

Pressed steel housing

Instead of a casting — a body pressed from steel sheet. The catalogue lists six flanged families (PF, PFD, PFL and their variants) plus the plummer block families PP and PPS.

The difference you see at once is mass: a PP 12 housing for an SA 201 bearing weighs 0.17 kg. A cast body of the same size weighs several times that. Sheet steel is, however, less rigid and takes shock loads poorly, so where something strikes or vibrates, the casting comes back.

Sheet steel where mass and cost matter. Casting where there are shocks.

A separate decision: how the bearing grips the shaft

With housings for insert bearings you also choose the shaft fixing, and it follows the direction of rotation. An eccentric collar (series HC and SA) is intended for a constant direction. Grub screws (UC and SB) take an alternating direction. An adapter sleeve (UK) suits higher speeds and changing directions — leave the bearing a small clearance on assembly.

All these designs are sealed on both sides and filled with lithium soap grease No 2, with a permissible range of −30 °C to +100 °C.