HGH vs HGW Blocks

HGH and HGW are the square and flange versions of the same HG block. They run on the same rail at the same size and carry the same rated load; what changes is the body, the mounting height and the way the carriage is bolted down. Choosing between them is a frame decision, not a load decision.

Side by side

At the same size the load rating is identical because the ball circuit and the rail profile are the same. The square block is taller and narrower; the flange block is lower and wider, with ears that spread the mounting holes. On a 25 mm size the difference is 40 mm against 36 mm in height, and 48 mm against 70 mm in width.

When the square block wins

Use HGH when the carriage plate is thick enough to take the bolts over the body, when height is not constrained, and when the block has to fit inside a narrow space. The square body is stiffer in torsion for its width, and it is easier to shim because the mounting face is directly under the load. On machining-centre axes with a cast iron saddle, HGH is the usual choice.

When the flange block wins

Use HGW when the carriage plate is thin, when the load sits away from the rail centreline, or when the frame cannot be raised. The wider bolt pattern spreads the load into the plate instead of concentrating it around the rail, and the lower body keeps the centre of gravity down. The CC variant is bolted from above and below, which matters on a carriage that is assembled from both sides.

The trade is height against footprint. A flange block needs lateral room for the ears; on a machine with two rails close together, the square block may be the only one that fits.

Mixing the two on one axis

It is possible to run one square and one flange block on the same carriage, and it is sometimes done to keep a low profile on one side. It is not a good default: the two bodies have different heights, so the carriage has to be machined to compensate, and the load share changes because the mounting points are not symmetric. If the design needs it, draw it that way rather than discovering it at assembly.

Same rail, same replacement rules

Both blocks use the same HGR rail and the same hole pattern, so a rail bought for one works with the other. Interchangeability follows the block, not the shape: up to accuracy P and preload ZA a block can be replaced on its own, while SP/UP and ZB are lapped as a set. The preload page explains where that line falls.

Models to compare

Square: HGH15CA, HGH20CA, HGH25CA, HGH30CA, HGH35CA, HGH45CA. Flange: HGW15CC to HGW45CC, plus HGW55CC and HGW65CC. Low profile: HGL30CA. Rails: HGR.

What changes in the stack when you swap

Swapping a square block for a flange block on the same rail moves three things: the assembled height, the width the carriage has to clear, and the bolt pattern. On a 20 mm size the height drops from 30 mm to 30 mm by coincidence at that size, but at 25 mm it drops from 40 to 36 mm, and the difference has to come out of the carriage plate or the machine loses its alignment. Measure the old block before ordering, not the model number: two blocks of the same size from different families are not the same height.

The bolt pattern is the second thing. The flange ears sit outside the rail centreline, so the tapped holes in the carriage move outward. A plate drilled for a square block will not take a flange block without new holes, and new holes near the old ones weaken the plate. This is a drawing change, not an assembly detail.

One practical check before ordering either shape: put the carriage plate on the bench and try the bolt positions. If the holes fall inside the rail footprint, the square block fits; if they fall outside it, the flange is the one the design intended. That single measurement avoids most of the swaps that come back.

FAQ