Reaming, Fits & Tolerances Chart | Ace Hardware Zimbabwe

Tolerance grades

ISO 286 tolerance grades - width of tolerance band in µm (0.001 mm)

Size mm	IT5	IT6	IT7	IT8	IT9	IT10	IT11
≤ 3	4	6	10	14	25	40	60
3 - 6	5	8	12	18	30	48	75
6 - 10	6	9	15	22	36	58	90
10 - 18	8	11	18	27	43	70	110
18 - 30	9	13	21	33	52	84	130
30 - 50	11	16	25	39	62	100	160
50 - 80	13	19	30	46	74	120	190
80 - 120	15	22	35	54	87	140	220
120 - 180	18	25	40	63	100	160	250
180 - 250	20	29	46	72	115	185	290
250 - 315	23	32	52	81	130	210	320
315 - 400	25	36	57	89	140	230	360
400 - 500	27	40	63	97	155	250	400

Hole and shaft limits

Hole limits (µm) - upper / lower

Size mm	H7	H8	H9	H11
≤ 3	+10 / 0	+14 / 0	+25 / 0	+60 / 0
3 - 6	+12 / 0	+18 / 0	+30 / 0	+75 / 0
6 - 10	+15 / 0	+22 / 0	+36 / 0	+90 / 0
10 - 18	+18 / 0	+27 / 0	+43 / 0	+110 / 0
18 - 30	+21 / 0	+33 / 0	+52 / 0	+130 / 0
30 - 50	+25 / 0	+39 / 0	+62 / 0	+160 / 0
50 - 80	+30 / 0	+46 / 0	+74 / 0	+190 / 0
80 - 120	+35 / 0	+54 / 0	+87 / 0	+220 / 0
120 - 180	+40 / 0	+63 / 0	+100 / 0	+250 / 0
180 - 250	+46 / 0	+72 / 0	+115 / 0	+290 / 0
250 - 315	+52 / 0	+81 / 0	+130 / 0	+320 / 0
315 - 400	+57 / 0	+89 / 0	+140 / 0	+360 / 0
400 - 500	+63 / 0	+97 / 0	+155 / 0	+400 / 0

Shaft limits (µm) - upper / lower

Size mm	d9	f7	g6	h6	k6	n6	p6
≤ 3	-20 / -45	-6 / -16	-2 / -8	0 / -6	+6 / 0	+10 / +4	+12 / +6
3 - 6	-30 / -60	-10 / -22	-4 / -12	0 / -8	+9 / +1	+16 / +8	+20 / +12
6 - 10	-40 / -76	-13 / -28	-5 / -14	0 / -9	+10 / +1	+19 / +10	+24 / +15
10 - 18	-50 / -93	-16 / -34	-6 / -17	0 / -11	+12 / +1	+23 / +12	+29 / +18
18 - 30	-65 / -117	-20 / -41	-7 / -20	0 / -13	+15 / +2	+28 / +15	+35 / +22
30 - 50	-80 / -142	-25 / -50	-9 / -25	0 / -16	+18 / +2	+33 / +17	+42 / +26
50 - 80	-100 / -174	-30 / -60	-10 / -29	0 / -19	+21 / +2	+39 / +20	+51 / +32
80 - 120	-120 / -207	-36 / -71	-12 / -34	0 / -22	+25 / +3	+45 / +23	+59 / +37
120 - 180	-145 / -245	-43 / -83	-14 / -39	0 / -25	+28 / +3	+52 / +27	+68 / +43
180 - 250	-170 / -285	-50 / -96	-15 / -44	0 / -29	+33 / +4	+60 / +31	+79 / +50
250 - 315	-190 / -320	-56 / -108	-17 / -49	0 / -32	+36 / +4	+66 / +34	+88 / +56
315 - 400	-210 / -350	-62 / -119	-18 / -54	0 / -36	+40 / +4	+73 / +37	+98 / +62
400 - 500	-230 / -385	-68 / -131	-20 / -60	0 / -40	+45 / +5	+80 / +40	+108 / +68

Worked example - 25 H7/g6: hole H7 for 18 – 30 mm = +21 / 0 µm → 25.000 – 25.021 mm. Shaft g6 = −7 / −20 µm → 24.980 – 24.993 mm. Clearance is 0.007 to 0.041 mm.

Fits and reaming

Choosing a fit (hole-basis)

Fit	Type	Assembly	Typical use
H11/c11, H9/d9	Loose clearance	Free by hand, large gap	Loose pins, agricultural and rough machinery
H8/f7	Running clearance	Turns freely, oil film	Plain bearings, shafts in bushes, pump shafts
H7/g6	Sliding clearance	Slides and turns with little play	Spigots, sliding gears, guided pins, piston-type fits
H7/h6	Locational clearance	Slides on by hand when oiled	Locating fits, gears and pulleys held by keys
H7/k6	Transition	Light mallet tap	Gears, pulleys, couplings; bearing seats with steady load
H7/n6	Transition (tight)	Press or heavy tap	Locating pins, bushes, motor shafts in rotors
H7/p6	Interference	Press or shrink fit	Bushes and sleeves that must not move; transmit torque without a key

Reaming allowance (machine reaming)

Reamer Ø mm	Stock to leave on diameter	Example: drill before reaming
up to 5	0.1 - 0.2 mm	4 mm reamer → 3.8 mm drill
5 - 10	0.2 mm	8 mm reamer → 7.8 mm drill
10 - 20	0.2 - 0.3 mm	12 mm → 11.8; 16 mm → 15.7 mm drill
20 - 30	0.3 - 0.4 mm	25 mm reamer → 24.6 mm drill
30 - 50	0.4 - 0.5 mm	40 mm reamer → 39.5 mm drill

Reaming tips

Run the reamer at about half to two-thirds of the drilling speed for the same size, and feed at 2 – 3 times the drilling feed. Too slow a feed rubs, glazes the hole and wears the reamer.
Too little stock also rubs. Too much overloads the reamer and gives an oversize, rough hole.
For an accurate position, spot and drill, then bore or use a slightly undersize drill so the reamer follows a straight hole.
Use cutting oil on steel. Ream cast iron and brass dry or with air.
Never turn a reamer backwards, even when withdrawing it: it chips the edges.
Hand reamers need 0.05 – 0.1 mm stock only. Use a tap wrench, keep the reamer square and turn steadily.
Standard machine reamers produce H7 holes in good conditions. Check the first hole with a plug gauge.