Split Bushing Tolerance and Shaft Fit: A Practical Sizing Guide for OEM Buyers
Specifying the inner diameter of a split bushing sounds simple, but a missing decimal or a wrong tolerance grade can cost an OEM buyer a full production run. This guide explains the three most common ISO tolerance grades for split bushings, how the longitudinal slot affects your inspection method, and how to choose the right shaft-to-bushing fit for your assembly.
1. Common Inner Diameter Tolerance Grades
The inner diameter (ID) of a precision split bushing is typically held to one of three ISO tolerance grades:
- H7 (±0.015 mm at 10 mm ID): the most common choice for sliding fits with precision shafts. Used in motor mounts, sensor housings, and pivoting joints.
- H8 (±0.022 mm at 10 mm ID): a relaxed grade for general industrial
applications where the bushing functions as a spacer or guide rather than a precision bearing surface.
- H9 (±0.036 mm at 10 mm ID): the loosest grade, used for cost-driven hardware where dimensional consistency matters less than assembly tolerance to surrounding parts.
Shangshi standard tooling holds H7 by default for split bushings under 25 mm ID, and H8 for sizes above 25 mm. Tighter tolerances (H6 or below) are available on request for prototype runs.
2. The Effect of the Slot on Measurement
Unlike a solid bushing, a split bushing has a longitudinal gap. Before measurement, the gap must be fully closed using a calibrated plug or arbor that matches the nominal ID. Measuring the split bushing without closing the slot will read 0.10 to 0.30 mm larger than the actual engaged ID - a common inspection mistake that leads to false rejections. Always request your supplier's measurement protocol and ask whether the inspection uses a closed-gap method.
3. Choosing the Right Shaft Fit
The relationship between the bushing ID and the mating shaft determines how the assembly performs:
- Clearance fit (shaft smaller than ID by 0.02 to 0.10 mm): the bushing slides freely on the shaft. Used for pivot joints, hinge pins, and adjustable mounts.
- Sliding fit (shaft smaller than ID by 0.005 to 0.020 mm): smooth linear motion with no perceptible play. Used in linear actuators, control linkages, and steering components.
- Press fit (shaft larger than ID by 0.005 to 0.020 mm): the bushing locks onto the shaft. Used when the bushing must rotate with the shaft and not slip.
For most automotive and industrial applications, a clearance fit on a tolerance-grade h6 shaft is the safe default. Confirm with your design team before locking the specification.
Need help specifying inner diameter tolerance, slot gap, or shaft fit for your split bushing order? Send your 2D drawing or a marked photo to ella.shangshi@gmail.com or WhatsApp +86 13968763726. Our engineering team will respond within 24 hours with a DFM-friendly tolerance suggestion and a quotation.
