What size is a 608 bearing? Dimensions and the hole to print

A 608 bearing is 8 x 22 x 7 mm: an 8 mm bore, a 22 mm outside diameter and a 7 mm width. ISO standardizes those boundary dimensions so bearings interchange between makers, which means a 608 from any brand fits the same pocket.

What size is a 608 bearing?

A 608 bearing has an 8 mm bore, a 22 mm outside diameter and a 7 mm width (0.315 x 0.866 x 0.276 in). Every 608 has those sizes, whatever the maker. A 608ZZ, a 608-2RS and an open 608 differ only in how the sides are closed.

Dimension	mm	in	Tolerance, ISO Normal class
Bore (d)	8	0.3150	0 to -0.008 mm
Outside diameter (D)	22	0.8661	0 to -0.009 mm
Width (B)	7	0.2756	0 to -0.12 mm
Edge chamfer (r)	0.3 minimum	0.0118
Inner ring shoulder (d1)	about 12.15	0.478
Outer ring recess for the shield or seal (D2)	about 19.2	0.756

The tolerances come from NTN’s tables for ISO Normal class, the same grade as ABEC-1. SKF makes its own 608 tighter: bore 0 to -0.007 mm, outside 0 to -0.008 mm, width 0 to -0.06 mm. Either way the outside is within 0.01 mm of 22 mm. The printed pocket decides the fit.

Load ratings differ a little by maker:

Rating	SKF 608	NTN 608
Basic dynamic load rating	3.45 kN	3.70 kN
Basic static load rating	1.37 kN	1.40 kN
Mass, open bearing	10.9 g	12 g

What is a 608 bearing?

A 608 is a single-row deep groove ball bearing. NTN’s bearing-number table decodes it digit by digit:

• 6: the type, a deep groove ball bearing.
• 0: the diameter series, which sets the outside diameter for a given bore. The matching width series (1) is left out of the number.
• 8: the bore in millimeters. Bore codes 1 to 9 are the bore itself. From 10 mm up the code changes: 00 means 10 mm and 01 means 12 mm.

Change the series digit and the bore stays 8 mm while the outside and width change. A 628 will not fit a 608 pocket:

Bearing	Bore	Outside	Width
698	8 mm	19 mm	6 mm
608	8 mm	22 mm	7 mm
628	8 mm	24 mm	8 mm

The 608 is also the skateboard bearing. Sector 9 says all standard skateboard completes use 608 bearings, two per wheel on an 8 mm axle, and that roller skates and inline skates use the same size.

608 bearing types: 608ZZ, 608-2RS and open

The suffix after 608 tells you what closes the sides. SKF and NTN use different letters for the same types:

What closes the sides	SKF	NTN	SKF limiting speed
Nothing (open)	608	608	48,000 r/min
Metal shields, both sides	608-2Z	608ZZ	38,000 r/min
Rubber seals, both sides, not touching the inner ring	608-2RSL	608LLB	38,000 r/min
Rubber seals, both sides, touching the inner ring	608-2RSH	608LLU	22,000 r/min

• 608ZZ has a metal shield on each side, fixed to the outer ring with a small gap at the inner ring. NTN rates shields “good” for dust and “poor” for water, with small torque and the same speed capacity as an open bearing.
• 608-2RS in a listing means rubber seals on both sides. Contact seals (SKF 2RSH, NTN LLU) get NTN’s best ratings for dust (“excellent”) and water (“very good”), but torque is higher and SKF cuts the limiting speed to 22,000 r/min. Non-contact seals (2RSL, LLB) keep the small torque and block more dust than shields, but NTN still rates them “poor” for water.
• Single-sided versions exist too: NTN’s 608Z has one shield.
• Flanged: NTN’s FL608 has a flange on the outer ring, 25 mm across and 1.5 mm thick. The flange locates the bearing in a printed part without a lip.

Does the ABEC rating matter for a 608?

No, not for a printed holder. ABEC is the American Bearing Manufacturers Association’s precision scale, and NTN’s catalog maps it onto the ISO 492 classes:

ABEC	ISO 492 class	Also written
ABEC-1	Normal	P0
ABEC-3	6	P6
ABEC-5	5	P5
ABEC-7	4	P4
ABEC-9	2	P2

The classes grade dimensional and running accuracy: how close the rings are to size and how true they run. Sector 9 sums it up as “precision and tolerance, not necessarily speed.” Even ABEC-1 holds the outside diameter within 0.009 mm, under a tenth of the 0.10 mm of interference a press fit uses.

What size hole do you print for a 608 bearing?

The hole for a 608 bearing should print at 21.90 mm for a press fit: 0.05 mm per side smaller than the bearing, or 0.10 mm on the diameter. For a slip fit it should print at 22.20 mm, 0.10 mm per side larger. Model it bigger by however much your printer prints holes small.

Fit	Per side	Total, on the diameter	Hole should print at	Holds the bearing by
Press fit	-0.05 mm (-0.0020 in)	-0.10 mm	21.90 mm (0.8622 in)	friction alone
Slip fit	0.10 mm (0.0039 in)	0.20 mm	22.20 mm (0.8740 in)	a lip on one side, a cap or clip on the other

Use the press fit when the bearing has to stay put on its own, and the slip fit when it must come out by hand. They are the press and snug presets of the tolerance calculator. The press value is QIDI’s lightest interference, from its published -0.05 to -0.15 mm per side. The slip value is the tight end of the 0.10 to 0.15 mm per side that the University of the Arts London Creative Computing Institute lab gives for snug pegs on its Bambu Lab H2D Pro printers. The bearing press fit guide gives the same fit for 623 to 6002 bearings.

Worked example: correcting for holes that print small

1. Model a 22.00 mm test hole in the holder’s material and orientation. Print it and measure it with the inside jaws of your calipers at three angles.
2. Say it averages 21.85 mm. Your holes print 0.15 mm small.
3. Model the press-fit pocket at 21.90 + 0.15 = 22.05 mm, or the slip-fit pocket at 22.20 + 0.15 = 22.35 mm.
4. Print a short ring with just that pocket and press a bearing in before you print the whole part.

That light press fit is enough. In a 2025 University of Kragujevac study, 6000-2RS bearings (26 mm outside) went into seats printed in PETG (glycol-modified polyethylene terephthalate) on a Bambu Lab X1E. The seat modeled 0.10 mm under the bearing printed at 25.86 mm, so the actual interference was 0.14 mm on the diameter.

Pressing that bearing in took about 200 N (the weight of 20 kg), and pulling it out took 225 N. After five cycles the seat showed no visible damage. A seat modeled 0.20 mm under needed about 450 N, and the authors favor the 0.10 mm seat for parts that must come apart.

Press the bearing in with a vise or a press, through a sleeve on the outer ring. NTN warns that force on the inner ring passes through the balls and can dent the raceways.

608 bearing holder: depth, lip and corner

• Depth: 7 mm, the bearing’s width. ISO Normal tolerance can make the ring up to 0.12 mm narrower but never wider, so the bearing will not stick out past the face.
• Lip: a ledge with an opening of 20 mm (0.787 in) or less. That is SKF’s maximum housing shoulder diameter for the 608, so the ledge bears on the outer ring. Keep it clear of the inner ring, which turns with the shaft and has a shoulder about 12.15 mm across.
• Corner: keep the corner between the pocket wall and the lip sharp. SKF allows a fillet of 0.3 mm at most there, the size of the bearing’s own edge chamfer. A larger fillet holds the bearing off the ledge.
• Orientation: print the holder with the bore axis vertical, so each layer draws the pocket as a closed circle. Bambu Lab’s X-Y hole compensation only acts on closed paths.
• First layer: put the lip on the bed side so the pocket opens upward. If the pocket opens onto the bed instead, elephant’s foot (first layers squashed wider than the rest) narrows its mouth. Chamfer that edge 0.4 mm x 45° or set elephant foot compensation to 0.15 to 0.25 mm, QIDI’s values.

What shaft goes through a 608 bearing?

An 8 mm steel dowel pin or ground rod fits the bore closely. An M8 bolt also goes through, with up to 0.24 mm of play on its thread. In ISO Normal class the bore measures 7.992 to 8.000 mm:

Through the bore	Diameter	Fit in a 608
8 mm dowel pin, ISO 8734 (tolerance m6)	8.006 to 8.015 mm	0.006 to 0.023 mm interference: press it in
8 mm ground rod, h6	7.991 to 8.000 mm	0.008 mm interference to 0.009 mm clearance: a push or slide fit
M8 x 1.25 bolt, 6g thread	7.760 to 7.972 mm across the thread	0.020 to 0.240 mm clearance
5/16-18 bolt, 2A thread	7.686 to 7.907 mm (0.3026 to 0.3113 in)	0.085 to 0.314 mm clearance
Printed shaft	model 8.10 mm (press) or 7.80 mm (slide), minus how much your pins print large	0.05 mm per side interference or 0.10 mm per side clearance

The M8 bolt is small on purpose. Bambu Lab’s wiki notes that the ISO 6g class “intentionally makes the thread slightly smaller to ensure easy assembly”. ASME B1.13M puts an M8 x 1.25 thread’s crests 0.028 to 0.240 mm under 8 mm.

The bearing then rests on those crests. That suits a spool holder or a wheel that only has to spin. For a belt idler or anything that must run true, use an 8 mm rod or dowel pin.

The printed shaft row uses the same press and snug fits with the bearing as the hole. In the tolerance calculator, put the clearance on the pin.

Clamp only the inner ring. A spacer or washer against the bearing should be 10 to 12 mm across for a 608-2Z and 10 to 10.5 mm for a 608-2RSH. Those are SKF’s shaft shoulder limits, and a wider washer can touch the shield or seal.

Where the bolt passes through printed parts rather than the bearing, give it an M8 clearance hole: 8.4 mm close or 9.0 mm normal, per ASME B18.2.8. The screw hole size calculator has the other sizes.

If the 608 bearing is too tight or too loose

• It won’t press in: measure the pocket. If it prints under 21.90 mm, model it bigger by the difference. Or set X-Y hole compensation to half the shortfall: Bambu Lab’s wiki says the hole diameter grows by twice the value, and the hole compensation calculator gives each slicer’s setting. Don’t force it. QIDI warns that past about 0.20 mm of interference a printed boss splits along a layer line.
• Tight only at the entrance: that is elephant’s foot. Chamfer the mouth or turn on elephant foot compensation, as above.
• It drops in or turns in the pocket: model the pocket smaller by the gap you measured. Or keep the pocket as a slip fit and hold the bearing with a lip and a cap.
• It sits crooked or sticks out: check the lip corner for a fillet over 0.3 mm and the pocket for its full 7 mm depth.
• It spins rough after fitting: it was pressed in through the inner ring, or a washer wider than SKF’s limit is touching a shield or seal.