SG Track Roller Bearings Size Chart: SG05 to SG66

SG series and closures

Series or suffix	Outer profile and use	Example
SG	Compact roller with a gothic-arch (peach-shaped) groove for round shafts and rails.	SG15 = 5 × 17 × 8
ZZ / 2RS	SG, LV and VW closures: metal shields / rubber seals	SG15 ZZ, SG15 2RS

Why SG and LFR rollers use a gothic-arch groove

The groove in an SG or LFR outer ring is not one circular arc. It is made of two arcs. Their centres are offset to the left and right, so the groove section is a pointed arch, also called a peach-shaped groove.

Each arc radius is slightly larger than the rail radius. On a round rail the roller therefore touches at two points, one on each side of the groove. The two contact lines are 60° apart, 30° on each side of the vertical. A small gap remains at the groove bottom.

What the two-point contact gives:

Guidance in both directions across the rail. The two contact points hold the roller centred on the rail. The roller carries the radial load and also keeps the carriage on line sideways.
Less sliding than a wrap-around groove. Both contact points are at the same rolling radius. A groove that wraps the rail along one full arc touches over a range of radii, so part of that contact must slide. A plain round groove with clearance slides even less under a pure radial load, but it does not hold the rail sideways.
Even load, less edge stress. The load is shared by two symmetric points, not carried at one point at the groove bottom or at a groove edge. Small mounting and rail errors therefore cause less stress concentration.
Adjustable preload. With one eccentric roller in the set, the two-point contact can be set to zero clearance or a light preload.

What it needs in return: the rail diameter must match the groove. On a rail that is too small the roller drops toward the groove bottom and loses its side location. On a rail that is too large it runs on the groove edges. The contact is a small point, so the rail must be hardened and ground.

The groove also takes axial force from both sides. For this reason SG and LFR rollers are both built on a double-row angular contact bearing with a thicker outer ring. The LFR sizes show it: an LFR5201 is 12 × 35 × 15.9 mm, a 5201 is 12 × 32 × 15.9 mm. An LFR5302 is 15 × 47 × 19 mm, a 5302 is 15 × 42 × 19 mm.

Groove profiles compared

Groove profile	Series	Runs on	Contact	What must match
Gothic arch (peach-shaped)	SG, LFR	Round shaft or rail with round races	Two points, 60° apart	Rail diameter to groove radius
V-groove	LV, VW	V-edge rail	Two flanks of the V	Rail angle to groove angle
Flat or crowned OD	Other track rollers	Flat track	One line or point	Needs a separate side guide

SG roller size chart

Each row is one size. Models that share the size are listed together and link to their model pages, where profile drawings and load ratings are given. Dimensions are in millimetres. Rollers with the same d × D × B can still have different profiles.

SG series

d	D	B	Models
4	12	4.6	SG05
4	13	6	SG10
5	17	8	SG15
5	22	8	SG66/5
6	21	11	SG66/21
6	22	8	SG66/3
6	22	10	SG66 SG66/1 SG66/2
6	24	11	SG20 SG24/3
8	22.5	14	SG22
8	24	11	SG24 SG24/1 SG24/2
8	25	17	SG20-D25 SG20/25
8	30	14	SG25
9	26	8	SG26
10	30	13	SG30
12	35	16	SG28
12	42	19	SG35

Dimensions are the same as on each model page. Profile drawings and load ratings are on the model pages.

Selection checks for track rollers

Start from the rail. Confirm groove angle or radius and the rolling-contact diameter before you compare model numbers.
Do not select a roller from OD and width alone. Two rollers with the same envelope can touch the rail at different points.
Decide how clearance or preload is set. A concentric roller gives the fixed datum. An eccentric mounting element adjusts the clearance.
Choose shields or seals by dirt, chips, coolant and speed. A seal is not always an upgrade, because it adds friction.

Custom track rollers

We make track rollers to drawing: special grooves, extended inner rings, non-standard widths, eccentric versions and polyurethane-covered rollers. Send the rail profile, shaft or stud size, load, speed and quantity, or an old sample.

Frequently asked questions

Why does an SG roller have a gothic-arch groove?

The two offset arcs make the roller touch a round rail at two symmetric points, 60° apart. This guides the roller sideways, slides less than a groove that wraps the rail, and lets an eccentric roller set zero clearance or light preload.

Can an SG roller be replaced by an LFR roller with the same OD?

Not on that basis alone. Groove geometry, contact diameter, inner-ring arrangement and adjustment method must also match.

What is the difference between a concentric and an eccentric roller?

A concentric roller sets the fixed datum. An eccentric mounting element is used to adjust system clearance or preload.

What should I measure on an old roller?

Measure bore, outside diameter and width, and record the outer profile, any groove angle or radius, the closure and the markings. A photo of the rail helps.

LFR gothic-arch track rollers →SG, LFR, LV, VW size chart in one table →Track roller series guide: SG, LFR, LV, VW →Choosing a track roller by rail profile →Eccentric track rollers and preload →Custom and polyurethane track rollers →All track roller bearings →

SG Track Roller Bearings: Size Chart