RexrothR162121420Size 25 Ball Runner Block, Slimline / Normal Length / High Body, 86.2 x 48 x 33.9 mm, Light Preload C1, Normal Accuracy — Guide Rail Not Included

Product Description

What this part is

A profiled-rail linear runner block: a hardened steel carriage with four rows of recirculating balls that rides along a matching profiled steel guide rail. The rail is bolted to the machine base, the block bolts to the moving carriage or table, and the ball circuits give you very low friction (coefficient around 0.002 to 0.003) with high rigidity in every direction except along the travel axis. This is the standard building block of a CNC machine axis, a gantry, a pick-and-place unit or a linear actuator.

Rail compatibility

Rail-to-block compatibility is the entire question with a runner block. This is a size 25 block, so it runs on a size 25 Bosch Rexroth profiled ball guide rail from the R1605 rail family — the companion rail series to the R1621 runner block series this part belongs to. Rexroth states in its own product data that runner blocks and guide rails can be combined as desired within each accuracy class, so any size 25 R1605 ball guide rail in accuracy class N will take this block, and a matched or serialised set is unnecessary. The rail hole pitch for this size is T = 60 mm, which is a quick way to confirm a rail already on the machine is the right size.

Profiled ball rail geometry is proprietary per maker, so the rail must come from the Rexroth R1605 family in size 25. An INA/Schaeffler KWVE25 carriage is the same nominal size 25 and is frequently offered as an alternative, but it runs a different rail profile. Match the rail to the block rather than the size number to the size number.

Decoding the order code

Rexroth uses a numeric material number (MNR) on the box plus a plain-language designation in its catalogue and configurator. Both are on this part.

R162121420: the Rexroth material number, printed on the carton label as MNR: R162121420. Blocks in this family carry material numbers beginning R1621; the companion ball guide rails begin R1605. The remaining digits index the size, design, preload and accuracy combination, and resolve to the designation below.

KWD-025-SNH-C1-N-1: Rexroth’s catalogue designation for this exact material number, which decodes cleanly.

KWD: ball runner block, Rexroth Ball Rail System.

025: size 25. This is the number that has to match the rail.

SNH: the body geometry, three letters in the order width, length, height. S = slimline (narrow) width, N = normal length, H = high body. So this is the slimline block. Slimline blocks suit installations where transverse space is restricted; they are through-bolted from above rather than flange-mounted, and Rexroth specifies the SNH as the higher-rigidity variant of the slim family with noticeably reduced frictional oscillation compared with the SNS.

C1: preload class C1, the light preload class. Preload matters more than most buyers expect: a preloaded block has no play and much better rigidity and positioning repeatability, at the cost of higher friction, more heat, and greater sensitivity to rail flatness. C1 is the sensible middle ground for general machine axes, with zero-preload and heavier-preload classes either side of it.

N: accuracy class Normal. The standard grade, appropriate for general automation and most machine axes; higher grades (H and above) exist for precision positioning work. Blocks and rails interchange freely within an accuracy class.

1: the ball-retention option, here the variant supplied without a ball chain. The balls are retained by the block’s own plastic retainers.

Carbon steel (CS) body, as printed on the carton (KUGELWAGEN CS / B.RUNNER BLOCK CS) — the standard material, distinct from the corrosion-resistant variant.

Seals, lubrication and the loose grease nipple

The block is supplied with SS standard seals and arrives pre-lubricated with Rexroth Dynalub 510 bearing grease plus a preservative. It ships with the straight lube connection loosely attached rather than fitted — that is the small grease nipple visible loose in the photographs, and it is a supplied part. The reference edge convention is front, with the block supplied in its standard body version.

Published ratings and mounting data

All figures below are Bosch Rexroth’s own configurator data for material number R162121420.

Size: 25.

Design: SNH — slimline width, normal length, high body.

Overall length of runner block: 86.2 mm.

Width of runner block: 48 mm.

Height of runner block: 33.9 mm.

Height of runner block with guide rail: 40 mm.

Guide rail hole pitch T: 60 mm.

Dynamic load capacity C: 28,600 N.

Static load rating C0: 35,900 N.

Dynamic torsional moment capacity Mt: 410 Nm.

Dynamic longitudinal moment capacity ML: 290 Nm.

Static torsional moment capacity Mt0: 510 Nm.

Static longitudinal moment capacity ML0: 360 Nm.

Maximum acceleration a max: 500 m/s².

Coefficient of friction: 0.002 to 0.003.

Permissible ambient temperature: −10 °C to +80 °C.

Body material: Carbon steel.

Seals: SS standard.

Self-alignment: None — this is a rigid, non-self-aligning block.

One important footnote that Rexroth attaches to the dynamic figures: the dynamic load capacity C and the moment capacities Mt and ML are calculated on a 100,000 m stroke life per DIN ISO 14728-1. Many specifications and competitor catalogues quote 50,000 m instead. To compare like with like against a 50,000 m figure, multiply C, Mt and ML by 1.26.

Quantity and configuration

Sold as individually boxed blocks; the carton label reads 1 Stück/Pcs. Each carton holds one block in its poly bag, the Rexroth instruction leaflet, and one loose straight grease nipple. Four identical blocks of the same size, design, preload class and accuracy class make up exactly one complete two-rail linear axis — two blocks per rail, two rails, the standard arrangement for a table, gantry beam or slide that has to resist moment loads as well as straight-line thrust. Sourcing matched blocks together guarantees the preload class and accuracy class are identical across the set, which is the thing that must match on an axis. Scope of supply is the runner block; guide rails are configured to length and ordered separately from the R1605 family.

Interchange guidance

The Rexroth material number R162121420 and the designation KWD-025-SNH-C1-N-1 refer to the same part; either will find it. The carton is also marked with a Bosch Rexroth instruction sheet number, R320103184 (2015-02 revision, replacing the 2010-02 issue) — that is the fitting instruction, and it is separate from the part number for the block. Neighbouring material numbers in the same family change one variable each: R162131420 is the same SNH-C1-N-1 configuration in size 35, and R162211420, R162231420 and R162271420 are other size and design combinations, so treat a nearby number as a different part. Same-size carriages from Schaeffler/INA (KWVE25 series), THK and HIWIN run on their own rail profiles. Bosch Rexroth linear motion products are sometimes still catalogued under the older Rexroth Star and Deutsche Star names.