THK2HR306RUUSeparate Type LM Guide Assembly, Two Carriage Blocks on a 440 mm Rail, High Accuracy Grade, User-Adjustable Running Clearance

Product Description

What this part is

This is a THK Separate Type LM Guide assembly — two carriage blocks with end seals supplied on a 440 mm rail, to high accuracy grade. The designation on the part is 2HR306RUU+440LH.

What the HR series is, and why it is different:
THK’s Model HR is a full-ball LM Guide of Separate Type. In THK’s own words, it “is an LM Guide that is capable of receiving an equal load in all four directions with parallel installation of two rails, has a low cross-sectional height, and allows the clearance to be adjusted.” Each rail carries two rows of balls at a 45° contact angle, full complement with retainer plates.

That adjustable clearance is the whole selling point and it separates the HR from every fixed-preload profile rail guide. On an HSR or SR block, preload is ground in at the factory and you take what you are given. On an HR, the two rails are mounted in parallel and the running clearance is set by how you position them, so you can dial in the fit at assembly — tighten it for rigidity, loosen it to accommodate a structure that is not perfectly true. For retrofit work on older machines, or for a frame that cannot be machined to profile-rail tolerances, that adjustability is worth a great deal. It is also why the HR carries no published preload grades: there is nothing to specify, because the user sets it.

One consequence you must design around: THK states that “one set of model HR means a combination of two LM rails and LM blocks used on the same plane.” The HR is fundamentally a two-rail product. A single rail cannot give four-way equal load on its own.

Identity — the designation as marked does not fully resolve:
Being straight rather than guessing: the size code “306R” does not exist in THK’s published HR range. THK’s HR sizes are 918, 1123, 1530, 2042, 2555, 3065, 3575, 4085, 50105 and 60125, where the two halves of the code are the section height M and the overall assembly width W0. The only published HR variants are T (ultra-heavy) and M (stainless) — there is no “R” suffix anywhere in the HR scheme.

Two readings are possible and both are stated honestly:

2HR3065UU+440L H — the marking is a transcription of HR size 3065 (30 mm section height, 65 mm assembly width). The published data for that size is given below.2HSR30R UU+440L H — the part belongs to the HSR family instead, where “R” is a real block type (narrow block with tapped holes). This reading has arithmetic behind it: HSR30 rail has an 80 mm hole pitch and 20 mm end dimension, so 5 × 80 + 2 × 20 = exactly 440 mm, a clean standard HSR30 rail length. 440 mm is not a clean HR3065 length.

The second reading is the more likely of the two, and it is reinforced by the fact that a single 440 mm HR rail is internally inconsistent with THK’s own statement that an HR set is two rails. Ask before ordering and we will read the markings off the rail and blocks directly. That takes a minute and settles it.

Published data for HR3065, if that is the reading:
Section height M: 30 mm; block width W: 40.3 mm; overall assembly width W0: 65 mmBlock length L with UU seals: 145 mm; block body L1: 90 mmBolt span C: 50 mm; taps 2 x M10, mountable top and bottomRail: W1 25 mm, W4 12 mm, M1 22.5 mm; hole pitch F 80 mm; hole 9 x 14 x 12 mm for M8Basic dynamic load rating C: 42.6 kN; basic static load rating C0: 44.4 kNStatic permissible moment MA and MB: 1.27 kN·m (one block) / 7.71 kN·m (two blocks) eachRolling elements: two rows of balls, 45° contact angle, full complement with retainer platesBlock mass 0.7 kg; rail mass 4.6 kg/m; maximum rail length 3000 mmService temperature −20 to 80 °C; accuracy grades Normal, H, P, SP, UP

MC is not published for the HR series, and THK explains why: “a moment in the MC direction can be received if two rails are used in parallel. However, since it depends on the distance between the two rails, it has been omitted.” Preload grades are likewise not published, because HR clearance is user-adjustable by design. Both gaps are real, not oversights.

Decoding the designation

2 — the number of LM blocks used on the same rail. THK places this field before the model number on Separate Type designations. So two blocks, not two assembliesHR — Separate Type full-ball LM Guide, adjustable clearanceUU — end seals fitted both ends. Note UU is end seals only; SS adds a side seal and DD is double seals+440L — a 440 mm rail supplied with the blocksH — high accuracy grade

Interchange guidance

Cross-references: 2HR306RUU+440LH, 2HR306RUU, HR306R, 2HR3065UU+440L, HR3065, HR3065UU, HR-3065, 2HSR30RUU+440L. Related: HR3065T (ultra-heavy variant), HR3065M (stainless), HR2555, HR3575. Sibling series with fixed preload: HSR30, SR30.

Central Surplus also stocks THK HSR25CA, HSR30CA, HSR30B, SR35W and SHW21CA blocks.