Types of fit

The three types of fit are:

1. Clearance: The hole is larger than the shaft, enabling the two parts to slide and / or rotate when assembled.

2. Location / transition: The hole is fractionally smaller than the shaft and mild force is required to assemble / disassemble

3. Interference: The hole is smaller than the shaft and high force and / or heat is required to assemble / disassemble

Clearance fits

Category	Description and usage	Example fit
Loose running	Larger clearance where accuracy is not essential - e.g. pivots, latches, parts affected by corrosion, heat, or contamination	H11/c11
Free running	Large clearance where accuracy is not essential and involves high running speeds, large temperature variations, or heavy journal pressures	H9/d9
Easy running	Moderate clearances with minimal requirements for accuracy - e.g. high running speeds, large temperature variations, high journal pressures, long shafts, pump or fan bearings	H9/e9
Close running	Small clearances with moderate requirements for accuracy - e.g. moderate running speeds and journal pressures, shafts, spindles, sliding rods	H8/f7
Sliding	Minimal clearances for high accuracy requirements, which can be easily assembled and will turn & slide freely - e.g. guiding of shafts, sliding gears, crankshaft journals	H7/g6
Location	Very close clearances for precise accuracy requirements, which can be assembled without force and will turn & slide when lubricated - e.g. precise guiding of shafts	H7/h6

For example, using an H8/f7 close-running fit on a 50 mm diameter:^[1]

· H8 (hole) tolerance range = +0.000 mm to +0.039 mm

· f7 (shaft) tolerance range = −0.050 mm to −0.025 mm

· Potential clearance will be between +0.025 mm and +0.089 mm

Transition fits

Category	Description and usage	Example fit
Tight fit	Negligible clearances which can be assembled or disassembled by hand - e.g. hubs, gears, pulleys, bushings, frequently removed bearings	H7/j6
Similar fit	Negligible clearance or interference fit which can be assembled or disassembled with a rubber mallet - e.g. hubs, gears, pulleys, bushes, bearings	H7/k6
Fixed fit	Negligible clearance or small interference fit which can be assembled or disassembled with light pressing force - e.g. plugs, driven bushes, armatures on shafts	H7/n6

For example, using an H7/k6 similar fit on a 50 mm diameter:^[1]

· H7 (hole) tolerance range = +0.000 mm to +0.025 mm

· k6 (shaft) tolerance range = -0.018 mm to +0.002 mm

· Potential clearance / interference will be between +0.043 mm and −0.002 mm

Interference fits

Category	Description and usage	Example fit
Press fit	Light interference which can be assembled or disassembled with cold pressing - e.g. hubs, bearings, bushings, retainers	H7/p6
Driving fit	Medium interference which can be assembled with hot pressing or cold pressing with large forces - e.g. permanent mounting of gears, shafts, bushes (tightest possible with cast iron)	H7/s6
Forced fit	High interference shrink fit requiring large temperature differential of parts to assemble, permanent coupling of gears and shafts that cannot be disassembled without risking destruction	H7/u6

For example, using an H7/p6 press fit on a 50mm diameter:

· H7 (hole) tolerance range = +0.000 mm to +0.025 mm

· p6 (shaft) tolerance range = +0.042 mm to +0.026 mm

· Potential interference will be between −0.001 mm and −0.042 mm.