THKHSR25A1KKC1LM Guide Block ONLY, Size 25 HSR, Square Flange, Four-Way Equal Load, Full Seal Package, C1 Light Preload — No Rail Included

Product Description

What this part is — and what is not in the box:
This is a THK LM Guide block only: the moving carriage of a size 25 HSR linear guide, with its ball complement, retainers, end plates and seals. No rail is supplied.

We are putting that first because a linear guide is a two-part product and the block is the half people accidentally buy on its own. A block without a rail cannot be used for anything — the recirculating ball tracks close through the rail’s ground raceways. Buy this if you are adding a second or third carriage to an HSR25 rail you already have, or replacing a block that has been crashed or contaminated on a machine whose rail is still true. If you need a working axis from scratch, you need a rail as well, cut to your length.

Four-way equal load — the reason the HSR series exists:
The HSR is THK’s global-standard full-ball LM Guide, and its defining feature is the 45° contact geometry: four rows of balls arranged so the block carries the same rated load in all four directions — downward, upward (lift-off), and laterally from either side. It also takes moment loads about all three axes.

That matters more than it sounds. A profiled rail with unequal ratings has to be oriented so its strong axis faces the load, which constrains the machine design and makes vertical or inverted mounting awkward. A four-way equal load block can be mounted in any attitude — horizontal, on its side, upside down, on a wall — and behave identically. It is why HSR guides turn up in gantries, vertical axes, robot arms and anywhere the load direction changes as the machine moves. Being full-ball (rather than caged-ball like THK’s SHS or SSR series), it is also the higher-rigidity, higher-capacity choice at a given size, at the cost of somewhat more noise and friction at speed.

Decoding the designation

HSR — THK full-ball LM Guide, four-way equal load type.25 — size 25. THK size codes correspond to a defined rail width and block envelope, so a size 25 block only fits a size 25 rail.A — block type: the square flange block, mounted from above or below through the flange. (THK’s other HSR block forms include B, R and LA/LB/LR variants with different flange shapes and lengths.)1 — the number of blocks. This designation describes one block, which is consistent with this being a single-block listing.KK — THK’s full seal package. THK’s contamination-protection codes run from SS (end seals only) through UU (end seals plus side seals) to the KK/ZZ level, which adds inner seals for the most complete sealing THK offers on this series.C1 — THK’s radial clearance / preload designation. In THK’s LM Guide scheme, clearance is specified as Normal, C1 or C0, with C1 denoting a light preload rather than running clearance.(GK) — a bracketed suffix carried on this part. We could not resolve it against any published THK designation table and are reproducing it exactly as marked rather than inventing a meaning for it.

Why the KK seals and C1 preload are the two things to check:
The seal package is a genuine specification, not a trim level. Linear guides fail on contamination far more often than they fail on fatigue. A ball rolling in a ground raceway will tolerate an enormous number of cycles; a single hard chip carried into the ball track will indent the raceway and end the block’s accuracy immediately. KK is the top of THK’s sealing range for this series, which is why you find it on machine tools running coolant and chips, and on woodworking and grinding equipment where fine abrasive dust is the enemy. If your machine is in that environment and the block you are replacing was KK, do not step down to SS or UU to save money — the seals are the reason the original lasted.

C1 light preload changes the machine’s behaviour, not just its feel. A guide with running clearance has a small dead band: the carriage can move slightly before the balls take load, which shows up as lost motion on reversal and as vibration under changing load. A preloaded block removes that clearance, so the carriage responds immediately and holds position under cutting or accelerating load. The cost is higher friction, higher heat and a shorter calculated life at a given external load, because the preload itself is a permanent internal load. If the block you are replacing on a multi-block axis was C1, match it — mixing preload classes on one rail loads the blocks unequally and the stiffest one takes the punishment.

Published data and what we have left blank

Series: HSR full-ball LM Guide, four-way equal loadSize: 25Block type: A (square flange)Blocks: 1Seal specification: KK (full seal package including inner seals)Clearance / preload: C1 (light preload)Rail: NOT included
We have not published block dimensions, load ratings or a static moment rating for this designation. THK’s own published range for size 25 HSR blocks spans a basic dynamic load rating from roughly 10.9 kN upward depending on the block form and length, and a corresponding static rating — but that is a range across the whole size-25 family, not a figure for the A-type block specifically, and quoting the top or bottom of a range as though it were this block’s rating would be misleading in either direction. THK publishes the exact figures per designation in its LM Guide catalogue. Ask us if you need the numbers and we will point you at the right table, or measure the block itself.

Fitting notes

Do not slide the block off a rail without a keeper: the ball complement is retained by the rail on an HSR block, and running it off the end lets the balls escape. If it arrives on a plastic dummy rail, leave the dummy in place until the block is on the real rail and transfer it directly. Mount the reference rail against a machined datum edge and pull it down progressively from one end; the accuracy of an LM Guide is the accuracy of the surface you bolt it to. Lubricate before first motion — a dry block on a dry rail scuffs within a few strokes.

Interchange guidance

Search forms include HSR25A1KKC1, HSR25A1KKC1(GK), HSR-25-A1KKC1, HSR25A1KK, HSR25A1, HSR25A, HSR25, HSR 25 A1 KK C1. Related THK designations at the same size: HSR25B (different flange form), HSR25R, HSR25LA and HSR25LB (long blocks, higher capacity), and the SS and UU seal variants of this same block. THK rails for size 25 are sold by length and by accuracy grade separately. Same-size profiled rail blocks from other makers — NSK LH25 / LAH25, Hiwin HGH25 / HGW25, IKO LWH25, Rexroth R1651 size 25 — are not interchangeable with a THK HSR25 rail. Profiled rail geometry is proprietary: a block and rail must be the same manufacturer and the same series.