Bronze bushing design guide – fits, tolerances and clearance
For designers specifying a cast bronze bush, maintenance engineers fitting one and buyers checking a drawing. Everything is in ISO fits with the inch rule of thumb in brackets. The starting point is how we deliver: bore E6, outside s6 (to Ø120) or r6, housing H7, shaft e7 – e8, per ISO 4379. Change any of these and the guide shows what follows.
A press-fitted bronze bush is a chain of three tolerances: the housing bore, the bush outside diameter and the bush bore, closed by the shaft. Interference between housing and bush holds the bush; the same interference shrinks the bore; what is left between shrunk bore and shaft is the running clearance. Get the chain wrong at any link and the bush either walks, seizes or wears out early.
Standard fit guidelines (ISO)
ISO 4379 fixes the fit system for copper-alloy bushes and it is what we machine to unless the drawing says otherwise. The housing is H7, the bush outside diameter s6 to Ø120 mm and r6 above (the larger the diameter, the smaller the relative interference), the bore E6 – deliberately wide so that after pressing it lands near H8 – and the shaft e7 for general duty or g7 where a smaller clearance is wanted. In inch practice the same fit is described as "0.0005 – 0.001 in of interference per inch of diameter" and "0.001 in of clearance per inch of shaft".
For your enquiry:Send your housing and shaft tolerances – we machine the bush to fit them, not the other way round.
| Element | ISO 4379 | Purpose | Inch rule of thumb |
|---|---|---|---|
| Housing bore | H7 | reference; chamfered edge, Ra ≤ 1.6 µm | nominal +0.0005 … +0.0015 in |
| Bush outside Ø | s6 (≤ Ø120) · r6 (> Ø120) | press fit that holds under load and heat | OD = housing + 0.0005 … 0.001 in per inch |
| Bush bore as delivered | E6 | closes to ≈ H8 when pressed | finish bore 0.001 – 0.002 in oversize |
| Shaft | e7 general · e8 heavy / hot / dirty · g7 precision | sets the running clearance | 0.001 in per inch of shaft (0.0015 – 0.002 heavy) |
| Flange Ø | d11 | clearance in the counterbore | — |
| Length | h13 | turned faces | — |
How much interference – by diameter
The table below is calculated from the ISO 286-2 deviations: s6 / r6 bush in an H7 housing. Read it as the range you will get with standard parts; a specific pair of measured parts lands somewhere inside it. The relative interference falls from 14 – 48 µm at Ø20 (0.07 – 0.24 %) to 31 – 106 µm at Ø200 (0.015 – 0.05 %), which is what a bronze bush needs: enough to stay put under the load and the thermal expansion of bronze (18 × 10⁻⁶ /K, 50 % more than steel), not so much that a thin wall yields.
Adjust when: the wall is thin (D/d < 1.15 – take the low end or p6), the housing is aluminium (expands with the bush – use r6 / s6 fully and add a keeper for heat), the housing is a thin ring that would stretch (reduce), or the position runs above 100 °C (bronze expands more than the steel housing and tightens further – the fit can be lighter). "Is 0.002 in a good press fit?" – for a 1 – 2 in bush, yes: 0.05 mm is inside the s6 / H7 band at Ø40 (18 – 59 µm); for a 4 in bush (Ø100: 36 – 93 µm) it is at the low end, for a 1/2 in bush (Ø12: 10 – 39 µm) too much.
For your enquiry:Give the housing material and the operating temperature if either is unusual.
Type a bore to show only that row; click a length to ask for a quote on that order code.
| Bore d | Outside Ø D | Interference min. – max. | Clearance min. – max. · e7 | e8 | g7 |
|---|---|---|---|---|---|
| 6 | 10 | 8 – 32 | — | — | — |
| 8 | 12 | 10 – 39 | 25 – 62 | 25 – 69 | 5 – 42 |
| 10 | 14 | 10 – 39 | 25 – 62 | 25 – 69 | 5 – 42 |
| 12 | 16 | 10 – 39 | 32 – 77 | 32 – 86 | 6 – 51 |
| 14 | 18 | 10 – 39 | 32 – 77 | 32 – 86 | 6 – 51 |
| 15 | 19 | 14 – 48 | 32 – 77 | 32 – 86 | 6 – 51 |
| 16 | 20 | 14 – 48 | 32 – 77 | 32 – 86 | 6 – 51 |
| 18 | 22 | 14 – 48 | 32 – 77 | 32 – 86 | 6 – 51 |
| 20 | 24 | 14 – 48 | 40 – 94 | 40 – 106 | 7 – 61 |
| 22 | 26 | 14 – 48 | 40 – 94 | 40 – 106 | 7 – 61 |
| 25 | 30 | 14 – 48 | 40 – 94 | 40 – 106 | 7 – 61 |
| 28 | 34 | 18 – 59 | 40 – 94 | 40 – 106 | 7 – 61 |
| 30 | 36 | 18 – 59 | 40 – 94 | 40 – 106 | 7 – 61 |
| 32 | 38 | 18 – 59 | 50 – 114 | 50 – 128 | 9 – 73 |
| 35 | 41 | 18 – 59 | 50 – 114 | 50 – 128 | 9 – 73 |
| 38 | 45 | 18 – 59 | 50 – 114 | 50 – 128 | 9 – 73 |
| 40 | 48 | 18 – 59 | 50 – 114 | 50 – 128 | 9 – 73 |
| 42 | 50 | 18 – 59 | 50 – 114 | 50 – 128 | 9 – 73 |
| 45 | 53 | 23 – 72 | 50 – 114 | 50 – 128 | 9 – 73 |
| 48 | 56 | 23 – 72 | 50 – 114 | 50 – 128 | 9 – 73 |
| 50 | 58 | 23 – 72 | 50 – 114 | 50 – 128 | 9 – 73 |
| 55 | 63 | 23 – 72 | 60 – 136 | 60 – 152 | 10 – 86 |
| 60 | 70 | 29 – 78 | 60 – 136 | 60 – 152 | 10 – 86 |
| 65 | 75 | 29 – 78 | 60 – 136 | 60 – 152 | 10 – 86 |
| 70 | 80 | 29 – 78 | 60 – 136 | 60 – 152 | 10 – 86 |
| 75 | 85 | 36 – 93 | 60 – 136 | 60 – 152 | 10 – 86 |
| 80 | 90 | 36 – 93 | 60 – 136 | 60 – 152 | 10 – 86 |
| 85 | 95 | 36 – 93 | 72 – 161 | 72 – 180 | 12 – 101 |
| 90 | 105 | 44 – 101 | 72 – 161 | 72 – 180 | 12 – 101 |
| 95 | 110 | 44 – 101 | 72 – 161 | 72 – 180 | 12 – 101 |
| 100 | 115 | 44 – 101 | 72 – 161 | 72 – 180 | 12 – 101 |
| 105 | 120 | 44 – 101 | 72 – 161 | 72 – 180 | 12 – 101 |
| 110 | 125 | 23 – 88 | 72 – 161 | 72 – 180 | 12 – 101 |
| 120 | 135 | 23 – 88 | 72 – 161 | 72 – 180 | 12 – 101 |
| 130 | 145 | 25 – 90 | 85 – 188 | 85 – 211 | 14 – 117 |
| 140 | 155 | 25 – 90 | 85 – 188 | 85 – 211 | 14 – 117 |
| 150 | 165 | 28 – 93 | 85 – 188 | 85 – 211 | 14 – 117 |
| 160 | 180 | 28 – 93 | 85 – 188 | 85 – 211 | 14 – 117 |
| 170 | 190 | 31 – 106 | 85 – 188 | 85 – 211 | 14 – 117 |
| 180 | 200 | 31 – 106 | 85 – 188 | 85 – 211 | 14 – 117 |
| 190 | 210 | 34 – 109 | 100 – 218 | 100 – 244 | 15 – 133 |
| 200 | 220 | 34 – 109 | 100 – 218 | 100 – 244 | 15 – 133 |
µm · s6 / r6 in H7 · bore ≈ H8 after pressing · ISO 286-2
No ISO 4379 size with this bore – send us the dimensions, we machine it to drawing.
The bore closes after pressing
A pressed bush transfers most of its interference to the bore: for a thin wall (D/d ≈ 1.1 – 1.2) reckon 80 – 100 % of the diametral interference, for a thick wall (D/d > 1.5) 50 – 70 %. Example: Ø40 × Ø48 × 40 bush, s6 in H7 – interference 18 – 59 µm, so the bore closes by roughly 15 – 55 µm. Delivered at E6 (Ø40: +50 … +66 µm) it lands at about 0 … +50 µm, close to H8 (0 … +39) – which is why ISO 4379 tolerances the bore E6 in the first place.
For a position where several bushes must line up, or the clearance must be closer than the sum of these bands allows, order the bore with 0.1 – 0.3 mm stock and ream or bore it in place after pressing. Machining a solid bronze bush in place is routine; a lined or sintered bush cannot be treated this way.
Running clearance
Cast bronze under grease wants more clearance than a rolling bearing engineer expects: 0.1 – 0.3 % of the shaft diameter, i.e. 40 – 90 µm at Ø30 and 100 – 250 µm at Ø100. Too little and the grease film cannot form, heat has nowhere to go and the bush seizes as the bronze expands; too much and the load concentrates on a narrow strip and the shaft hammers. The table below gives the clearance of a bore at about H8 after fitting against an e7 shaft; take e8 (about 50 % more) for hot positions, misalignment and dirty grease, g7 for oil-lubricated precision spindles.
"How much clearance for a bronze bushing?" – start at 0.001 in per inch of shaft (0.1 %), add 50 % for heat, dirt or an aluminium bronze / C86300 bush, which do not conform. Never run a bronze bush at zero clearance.
Press-fit calculator
Enter bore and outside diameter (any size from 6 to 250 mm) and pick the shaft tolerance. The calculator reads the ISO 286-2 deviations for s6 / r6 in H7, E6, H8 and e7 / e8 / g7 and prints the interference, the expected bore after pressing and the running clearance. It uses standard tolerances, not measured parts; for a critical position measure the housing and shaft and send the numbers.
Wall thickness, chamfers and lead-in
ISO 4379 gives three walls per bore: at Ø25 the outside diameters are 28, 30 and 32 (walls 1.5, 2.5 and 3.5 mm), at Ø100 they are 110, 115 and 120 (5, 7.5 and 10 mm), at Ø200 they are 210, 220 and 230. The thin wall suits space-limited housings and thin-wall pressing; the medium and thick walls carry heavier housings, edge loading, grooves and re-machining allowance. Below about 1.5 mm a cast bronze bush is difficult to press without collapse; above about 0.15 × d the bush stops conforming and the housing must be accurate.
Chamfers: 45° × 0.3 – 2 mm on the outside for lead-in, 15° × 1 – 5 mm on the bore to guide the shaft and keep grease from being wiped out (values per ISO 4379). Chamfer the housing edge too – a sharp housing edge shaves the bush and starts a crack. Press from the chamfered end, with the flange side first on flanged bushes.
Installation methods: press, shrink fit, adhesive
Press fit: a hydraulic or arbor press with a stepped mandrel that pilots in the bore and pushes on the end face; align the bush square before it enters; press steadily, never hammer on the bronze (it flares the end and cracks the wall). Press force estimate: F ≈ μ × p × π × D × L, with μ ≈ 0.15 for dry bronze on steel and p the contact pressure from the interference – we calculate it for your sizes on request; light oil on the outside diameter halves the force and does not loosen the fit.
Shrink fit: heat the housing (steel: up to 150 °C is harmless; 100 °C at Ø100 opens the bore by 0.12 mm) or cool the bush in dry ice (−78 °C shrinks a Ø100 bronze bush by about 0.18 mm) and drop the bush in; the fit is then the full interference without any pressing damage – the usual method above Ø150 mm. Do not heat a bronze bush above 250 °C.
Adhesive: an anaerobic retaining compound can replace part of the interference (a slide fit plus adhesive) for thin housings, aluminium housings or repairs of oversize bores; it does not survive above about 150 °C or repeated shock and is not a substitute for a proper press fit on a heavily loaded pin. Anti-rotation: the flange, a dowel or a grub screw in a drilled spot when the fit alone is doubtful.
Shaft: hardness and surface finish
The shaft must be the harder partner. Leaded tin bronze and gunmetal (55 – 75 HB) run on unhardened or quenched-and-tempered steel of 150 – 200 HB; tin and phosphor bronzes (90 HB) want 250 HB or better; aluminium bronze and C86300 (150 – 225 HB) need a hardened and ground shaft of 300 HB minimum, typically 45 – 55 HRC, or hard chrome. Surface finish Ra 0.8 µm or finer, Ra 0.4 for the hard alloys at higher speed; a rough shaft acts as a file on the bronze, a polished shaft carries the grease film. Stainless shafts run well on gunmetal and tin bronze; on aluminium bronze they gall unless hardened.
Large-diameter bushings above Ø200 mm
Above the ISO series the relative interference keeps falling (r6 in H7 gives 0.015 – 0.05 %) and shrink fitting replaces pressing. Large bushes are machined with a wall of 5 – 10 % of the bore, the outside to r6 or to a slide fit with a keeper, and the bore often finished in place after the housing is bored. Walls flex during transport: measure the bush and the housing before fitting, and expect a Ø500 bush to be 0.1 – 0.2 mm out of round when unrestrained – it becomes round in the housing. Half bearings and segmented rings are made where a one-piece bush cannot be fitted.
Important things to remember
Eight points that cover most fitting failures:
- Housing H7, bush s6 / r6, bore E6 as delivered, shaft e7 / e8 – or say what you use instead
- Chamfer the housing edge and press from the chamfered / flanged end with a mandrel – never hammer
- Expect the bore to close by 50 – 100 % of the interference; measure it after pressing on precision positions or order it for finishing in place
- Running clearance 0.1 – 0.3 % of the diameter; more for heat, dirt and hard alloys
- Shaft harder than the bush: plain steel for 660 and LG2, hardened 300 HB+ for aluminium bronze and C86300
- Shaft Ra 0.8 µm or better; a rough shaft destroys any bronze
- Oil hole and grooves outside the load zone; relubricate before the old grease is gone
- Above Ø150 shrink-fit instead of pressing; above Ø200 consider finishing the bore in place
Frequently asked questions
Is 0.002 in a good press fit for a bronze bushing?
For bushes of 1 – 2 in outside diameter, yes – 0.05 mm sits inside the ISO s6 / H7 band (18 – 59 µm at Ø40). For a 4 in bush it is at the low end (s6 / H7 gives 36 – 93 µm at Ø100), for a 1/2 in bush too much (Ø12: 10 – 39 µm). Scale interference with diameter, not as a fixed number.
How much clearance for a bronze bushing?
Start at 0.1 % of the shaft diameter (0.001 in per inch) – 30 µm at Ø30 – and add 50 % for heat, dirty grease, misalignment or a hard alloy. With ISO parts an H8 bore after fitting against an e7 shaft gives 40 – 94 µm at Ø30, which is the right range for grease.
Do I ream after pressing?
Not for a general-duty position with an e7 shaft – the E6 bore closes to about H8 and that is the clearance you want. Ream or bore in place when several bushes must be aligned, when the fit must be closer, or when the housing is oversize or out of round; order the bore with finishing stock for that.
H7 housing – what bushing OD?
s6 up to Ø120 mm and r6 above, per ISO 4379; both are in the size chart and are what we deliver. For a thin-wall bush or a thin housing ring, p6; for an aluminium housing keep s6 and add a keeper for heat.
Can I use adhesive instead of a press fit?
For thin or aluminium housings, repairs of oversize bores and lightly loaded positions below 150 °C, a slide fit with an anaerobic retaining compound works. For heavily loaded pins, shock or heat, no – use the press or shrink fit and, if in doubt, a dowel or grub screw.
Metric or inch tolerance classes on my drawing?
Either. We machine to the ISO classes by default and to inch limits when the drawing gives them; the cross-walk is above. For inch drawings without tolerances we apply the ISO 4379 classes to the inch nominal and note it in the quotation.
Quote bushings to these dimensions
Send housing and shaft sizes with tolerances, length, alloy and quantity – we machine the bush to fit and confirm the clearance you will get.