Knowledge · Linear Motion
Rexroth type code explained: decoding KWD, FNS, SNS and the R16 numbers
A Bosch Rexroth runner block carries its full configuration in the type code: KWD-025-FNS-C1-N-1. Six fields, from the family to the seal, describe the block in full; read them and you order the right part without a PDF catalog. The R16 part number next to it, by contrast, is just an ordering number: preload and accuracy live in the code, not in the digits.
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The type code at a glance
The type code of a Rexroth ball runner block is a fixed chain of six fields. Take KWD-025-FNS-C1-N-1: each position stands for exactly one property, namely family, size, carriage form, preload, accuracy, seal. Read the chain left to right and you have described the block in full without opening a catalog.
KWD is the family: the ball runner block of the BSHP ball rail system. Its matching rail is called KSA. The three digits that follow are the size (here 25). The three letters are the carriage form. The remaining fields set preload, accuracy class and seal design.
| Field | Segment | Value | Meaning |
|---|---|---|---|
| Family | KWD | ball runner block | block of the BSHP system (rail: KSA) |
| Size | 025 | 25 | width/series, here size 25 |
| Carriage form | FNS | flange, normal, standard height | mounting, block length, block height |
| Preload | C1 | moderate preload | internal preload of the block |
| Accuracy | N | Normal | tolerance class for height and running |
| Seal | 1 | standard | wiper/seal design |
Reading the carriage form: three letters
The three carriage-form letters follow a fixed grammar. Position 1 describes the mounting, position 2 the block length, position 3 the block height. From that system you can derive every common block: FNS is a flange block of normal length in standard height, SLH a narrow, long block in high design.
Mounting decides the fastening direction: the flange block (F) is bolted through the flange from above or below, the narrow block (S) is bolted from the top into the block body and builds more compactly. Length drives load capacity: a long block (L) carries more than a normal (N) or short (K) one at the same size. Height adjusts the connecting dimensions.
| Position | Letter | Meaning |
|---|---|---|
| 1: mounting | F | flange (bolted through the flange) |
| 1: mounting | S | narrow (bolted from the top, compact) |
| 2: length | N | normal (standard length) |
| 2: length | L | long (more ball rows, higher load rating) |
| 2: length | K | short (compact design) |
| 3: height | S | standard height |
| 3: height | H | high |
| 3: height | N | low |
| Form | Mounting | Length | Height |
|---|---|---|---|
| FNS | flange | normal | standard height |
| FLS | flange | long | standard height |
| FKS | flange | short | standard height |
| SNS | narrow | normal | standard height |
| SLS | narrow | long | standard height |
| SKS | narrow | short | standard height |
| SNH | narrow | normal | high |
| SLH | narrow | long | high |
Preload: C0, C1, C2, C3
Preload is the internal tension of the block against the rail. The concrete preload force Fpr is defined by Rexroth per block in the catalog. More preload means higher stiffness and less play, but also more friction and shorter service life. Preload should not exceed one third of the external bearing load. Which class fits your application is covered in choosing preload correctly.
| Code | Preload | Typical application |
|---|---|---|
| C0 | no preload | low friction, easy running, higher mounting tolerances |
| C1 | moderate | precise guidance, low external loads, high stiffness |
| C2 | average | high external loads and high stiffness, also single-rail |
| C3 | high | maximum stiffness, high moment and alternating loads |
Accuracy: N, H, P, XP, SP, UP
The accuracy class limits the tolerance of the height dimension and the parallelism of block and rail. From N to UP the tolerances tighten, the price rises, the choice narrows. N and H cover general machine building, P through UP are for precision and measuring applications. The full tolerance table is in accuracy classes in detail.
| Code | Class | Application range |
|---|---|---|
| N | Normal | general machine building, standard applications |
| H | High | tighter tolerance, demanding machine building |
| P | Precision | precision applications with tight height dimension |
| XP | Extra precision | very tight tolerances, dynamic precision axes |
| SP | Super precision | machine tools, high positioning accuracy |
| UP | Ultra precision | maximum accuracy, metrology and fine machining |
The R number: a part number, not a second type code
Alongside the type code, every block carries a ten-character Rexroth part number, the R16 number, for example R165121421. This number is unique per variant: the same size with a different preload, accuracy or seal yields a different R number. It is an ordering number, not a second type code. Preload and accuracy cannot be read from the digits.
A coarse pattern does exist: the number stem (the leading characters) groups by carriage form, for example R1622 for SNS or R1651 for FNS. Do not read more than that out of the digits. For preload, accuracy and seal, rely on the type code, and when ordering, verify the full part number of the specific variant.
Three type codes decoded
The following three variants come straight from the PTS range. Watch the R numbers: both SNS blocks share the stem R1622, while the FNS block sits in the stem R1651. The full number also carries size, preload and seal, which is why only the part number of the specific variant counts when ordering.
| Type code | R number | Size | Carriage form | C dyn. (C100) | C0 stat. |
|---|---|---|---|---|---|
| KWD-025-FNS-C1-N-1 | R165121421 | 25 | flange, normal | 28.6 kN | 35.9 kN |
| KWD-015-SNS-C1-N-1 | R162211420 | 15 | narrow, normal | 9.9 kN | 12.7 kN |
| KWD-035-SNS-C1-N-1 | R162231420 | 35 | narrow, normal | 51.8 kN | 80.9 kN |
Type code decoded, now configure the system
Turn the code into a complete system: pick size, carriage form, preload and accuracy, add the rail cut to length and see the matching load ratings and price for every type code.
Prices and stock are visible in the catalog without signing in.
And the rail? KSA and the R1605 pitch
The rail for the block is the KSA ball rail. It too carries an R16 part number, and every standard rail of this series begins with R1605. That R1605 identifier stands for the pitch, that is the hole spacing of the mounting bores. The same rail type can exist in a different R-number series with a different pitch. So match the pitch before every reorder; the size alone says nothing about it.
Three rules govern the pairing: the accuracy class of the rail must match that of the block. The size must match. The carriage form of the block is free, every form runs on the rail of the same size. Whether with a cover strip or with fastening from above is decided at the rail step, because the cover strip is a separate rail part number and cannot be added later. Cutting the rail to length and planning the edge distance then follow as a separate step.