Key takeaway: Most “the linear guide doesn’t fit” cases are not product-quality issues. They usually happen because the rail series is different, the brand has small dimensional differences, or the buyer did not send complete size information. If you confirm the size in advance — either by model/drawing or by clear dimension photos — you can avoid wrong hole pitch and height mismatches, even for cross-border orders.

• Automation/system integrators replacing an original rail on a machine
• Projects that must stay compatible with HIWIN, THK, PMI or other global brands
• Frames that are already drilled and are very sensitive to rail height or hole pitch
• Buyers ordering from online platforms but unsure if the rail will actually fit

From the outside, two rails can both say “12 mm”, but that doesn’t mean they can be mounted to the same machine. Typical reasons:

1. Same width, different series. For example, MGN12 and MGH12 are both 12 mm class, but block height, rail section, and hole spacing are different.
2. Brand-to-brand micro differences. Many local rails are “close to” HIWIN/THK dimensions, but not 100% mirrored. If the base plate is already drilled, even 0.2–0.5 mm can make installation tight.
3. Online titles are too generic. Product titles often say “MGN12 linear guide”, but the real decision makers are in the detail page: hole pitch (P), hole type, rail height (H), block mounting height (H1).
4. Retrofit jobs are non-standard. Old machines, imported equipment or extended modules often mix dimensions. Guessing the model is risky.

If you want to reduce installation failures, build this as your standard workflow.

Send any of these:

• Full model, e.g. “HIWIN MGN12H”, “THK SSR15XW”, “PMI MSA15E”
• PDF installation drawing from your customer
• Old part number from previous purchase

The supplier can trace the installation dimensions from this and propose a compatible or equivalent rail+block set. This shifts the size judgment to the supplier — you only need to confirm the drawing they send back.

For retrofit or unclear cases, don’t guess the model. Take clear photos with a ruler instead. Try to capture:

• Rail width (W)
• Center-to-center hole pitch (P), preferably two holes in one photo
• Hole type (countersunk / through hole)
• Rail height and block mounting height (to avoid interference)
• Bottom hole pattern of the old block if you are replacing a foreign brand

With this, the supplier can choose the closest series from their catalog and send you a dimension sheet for confirmation. That keeps responsibilities clear on both sides.

• Same series name ≠ identical dimension. MGN/MGH/HG/EG exist in many brands, but small details and tolerances may differ. Always review the drawing.
• Buy rail and block as one set if possible. Mixed brands can “fit”, but smoothness and lifetime may drop.
• If your frame is already drilled, start from the hole drawing. That is your real constraint.

Even with pre-checks, on-site conditions can still change. Clear policies make cross-border buyers more confident:

• Allow changing rail length or block type within the same batch
• Provide hole drawings or 2D/3D files so the customer can pre-machine the frame
• If the mismatch is caused by unclear supplier description, the supplier covers the freight

Publishing this on your product page will directly help conversion.

The safest rule is: “If you have the model, check by model. If you don’t, send dimensions. Only order after the drawing is confirmed.” If you follow this, installation failures for linear guides will drop sharply.