HG vs EG Linear Guides

HG and EG are both four-row ball guides at 15 to 30 mm, but they are built for different jobs. HG is the machine-tool guide: higher body, higher rail, four-point contact, more load. EG is the low-assembly guide: lower body, lower rail, two-point arc contact, and a self-aligning behaviour that absorbs mounting error. They do not share a rail and are not interchangeable.

Side by side

The pattern is consistent: at every size the EG is 4 to 7 mm lower in body height and lower on the rail, and its dynamic load is roughly 60% of the HG figure. On 25 mm the HG block is 40 mm high and rated 26.48 kN; the EG is 33 mm and 16.27 kN. That is not a quality difference: it is the geometry of the contact.

Why EG is lower and less stiff

The EG uses an arc raceway with two-point contact, which lets the block self-align as it moves; the HG uses a single-arc four-row design with contact in four directions. The EG geometry trades some rigidity for tolerance of mounting error and a lower overall height, which is why it is used on frames that are welded, sheet-metal or otherwise not hand-scraped. The HG assumes a machined bed and rewards it with stiffness.

The lower rail also matters for stack height. Where the frame is fixed and the carriage has to sit close to the bed — laser heads, packaging pushers, high-speed pick-and-place — the EG profile saves 3 to 7 mm at the body and a similar amount at the rail. On a machine with a defined working height, that is the difference between fitting and machining the frame.

Preload and accuracy are not the same between the two

The grade letters look identical and the meaning is not. On the EG series the preload bands are Z0 0–0.02C, ZA 0.03–0.05C and ZB 0.06–0.08C; the HG series uses 0.05–0.07C for ZA and 0.10–0.12C for ZB. So “ZA” on an EG block is a lighter preload than “ZA” on an HG block of the same size, and a quotation that just says “ZA” without the series is ambiguous.

Accuracy grades run C to UP on both, with the interchangeable limit at P and the matched sets for SP/UP. The tolerances are quoted per size and per length, so they are read from the datasheet rather than assumed to be equal across the two families.

When to choose EG

Choose EG when the frame is not precision-machined, when the carriage has to sit low, or when the axis runs fast with a light load. Packaging machines, laser cutters, dispensing heads and high-speed transfers are the usual applications. The self-aligning behaviour means the mounting surface does not have to be perfect, which reduces machining cost on the frame — often more than the price difference between the two guides.

When to stay with HG

Stay with HG when the cut is heavy, when the bed is machined, or when the axis has to hold position under a reversing load. Machining centres, grinders and heavy gantries are HG territory. If an axis is borderline, compare the load first: the EG at 30 mm is 23.70 kN against 38.74 kN for HG, so a machine designed around HG load can rarely drop to EG without going up a size.

Do not mix the rails

HG runs on HGR rails and EG runs on EGR rails. The nominal widths overlap but the profiles differ, so an HG block will not run on an EGR rail and vice versa. A “drop-in replacement” between the two families does not exist; what exists is a choice at design time. Within a family the interchangeable rules apply as usual, and the preload page explains where the block can be bought separately.

Models to compare

HG: HGH15CA, HGH25CA, HGH30CA, HGW25CC. Low profile HG: HGL30CA. EG: EG series. Rails: HGR. Selection help: selection guide.

A practical test when both look possible: measure the straightness of the bed first. If it is within a few hundredths over a metre, HG will hold its grade and the extra stiffness is free. If it is not, EG will follow the frame less harshly and the axis will run smoother — but the load has to fit, so go up a size rather than expecting EG to carry an HG load.

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