Guide
What retaining ring groove dimensions and edge margin should a shaft or bore drawing call out?
A retaining ring groove is the turned or bored annular slot that seats a snap ring (circlip) on a shaft or in a housing bore, and its diameter, width and distance from the end of the part decide whether the ring carries its rated thrust load or rolls out of the groove.
By Saola Manufacturing engineering team · Published · Updated
Most groove problems are not exotic. The ring is a catalog part, the groove is copied from the ring maker’s table, and then something small goes wrong between the table and the turned shaft: the groove is dimensioned from the wrong face, the shaft is shortened late in the design and the groove ends up too close to the end, or a plating callout quietly eats the width clearance. This guide covers the four numbers a groove drawing must carry, why the edge margin governs the thrust load, how to tolerance and locate the groove, and how to write it on a drawing and RFQ so an overseas lathe shop makes exactly what the ring needs.
On this page
What does a retaining ring groove have to control?
Four things: the groove diameter, which sets how far the ring sits into the part; the groove width, which must clear the ring thickness; the edge margin, which is the solid material between the groove and the end of the part; and the edge and corner geometry on the loaded side. A drawing that only gives diameter and width is half a specification.
The groove diameter (d2 in the DIN tables) fixes the groove depth and therefore how much of the ring cross-section stays engaged under load. It also fixes the ring’s installed tension: on a shaft, an external ring sits in the groove with a slight grip, so a groove cut too deep lets the ring sit loose and rattle, while one cut too shallow leaves the ring opened past its design state and reduces the shoulder it presents to the retained part.
The groove width (m) only has to clear the ring thickness. It is not a fit; extra width shows up as axial play in the assembly, and too little width means the ring will not seat at all. The edge margin (n) is the dimension most often forgotten, and it protects the part of the assembly that usually gives way first under thrust: the groove wall, which yields outward long before a hardened ring shears.
Finally, the side of the groove that the ring pushes against should be square and sharp-cornered at the groove opening, while the groove bottom carries a small radius for fatigue. The fillet vs chamfer guide covers the stress side of that trade-off in general; for a groove, the rule is simply that the loaded wall must stay square.
What are the standard groove dimensions for common shaft and bore sizes?
For metric circlips, the groove is defined by DIN 471 for shafts and DIN 472 for bores, and the table below lists the groove diameter, width, depth and minimum edge margin for the most common sizes. Copy the row for your nominal diameter onto the drawing rather than scaling the ring.
The groove depth t is tabulated in both standards and equals half the difference between the nominal shaft or bore diameter and the groove diameter; it is worth reading because it explains the edge margin column next to it. Note that the shaft groove is smaller than the shaft and the bore groove is larger than the bore, so the depth is always measured into the parent material.
| Standard and nominal diameter | Ring thickness s | Groove diameter d2 | Groove width m (H13) | Groove depth t | Minimum edge margin n |
|---|---|---|---|---|---|
| DIN 471 shaft, 10 | 1.00 | 9.6 | 1.10 | 0.20 | 0.6 |
| DIN 471 shaft, 15 | 1.00 | 14.3 | 1.10 | 0.35 | 1.1 |
| DIN 471 shaft, 20 | 1.20 | 19.0 | 1.30 | 0.50 | 1.5 |
| DIN 471 shaft, 25 | 1.20 | 23.9 | 1.30 | 0.55 | 1.7 |
| DIN 471 shaft, 30 | 1.50 | 28.6 | 1.60 | 0.70 | 2.1 |
| DIN 471 shaft, 40 | 1.75 | 37.5 | 1.85 | 1.25 | 3.8 |
| DIN 472 bore, 25 | 1.20 | 26.2 | 1.30 | 0.60 | 1.8 |
| DIN 472 bore, 30 | 1.20 | 31.4 | 1.30 | 0.70 | 2.1 |
| DIN 472 bore, 40 | 1.75 | 42.5 | 1.85 | 1.25 | 3.8 |
| DIN 472 bore, 47 | 1.75 | 49.5 | 1.85 | 1.25 | 3.8 |
Read the last two columns together. In every row, the minimum edge margin is about three times the groove depth. That ratio is the most useful thing to remember from the table, because it lets you sanity-check a groove on a drawing without opening the standard: if the material between the groove and the end of the shaft is less than three groove depths, the groove is too close to the end.
The groove diameter also carries a tolerance in each standard (an h-grade for shaft grooves and an H-grade for bore grooves, loosening as the size grows). Copy that tolerance from the same edition you cite instead of leaving it to the title-block default, which was not written with the ring in mind.
Why does the retaining ring groove edge margin set the thrust load?
Under axial load the ring presses on the outer wall of the groove, and that wall is a short cantilever of parent material that can yield or shear off toward the end of the shaft. DIN 471 and DIN 472 therefore give two load ratings, FN for the groove and FR for the ring, and in the normal-type rows above the groove rating is the lower one: for a 20 mm shaft per DIN 471, 5.06 kN for the groove against 17.1 kN for the ring.
The groove rating in a manufacturer’s table is only valid when three conditions hold: the edge margin is at least the tabulated minimum, the shaft material has at least the yield strength the table assumes, and the part being retained sits against the ring with a square corner. Break any one of them and the real capacity drops below the catalog value without anything looking wrong on the drawing.
The third condition is the one designers miss. If the retained bearing or hub has a large chamfer or radius on the face that touches the ring, it contacts the ring near its outer edge instead of near the shaft. The ring then tilts (dishes) in the groove, the effective lever arm on the groove wall grows, and the ring can roll out at a fraction of its rating. DIN 471 and DIN 472 show the size of that effect: they tabulate a corner chamfer or radius g on the abutting part and a separate ring rating FRg that applies with it. For a 20 mm shaft per DIN 471 that is g = 1.5 mm and 3.85 kN, against 17.1 kN for a square corner. If your bearing’s corner is larger than g, add a square-cornered spacer washer between the bearing and the ring.
Edge margin is also where late design changes bite. A shaft shortened to save length, or a groove moved outboard to make room for a seal, can leave the groove within one or two groove depths of a chamfered end. Re-check the three-to-one relationship every time the shaft length or groove location changes, and count the end chamfer against the margin, because the chamfer removes material from exactly the wall that carries the load.
How tightly should the groove be toleranced and located?
Tolerance the groove width and diameter exactly as the ring standard does, and spend your tight tolerance on the axial location of the loaded groove wall instead. That one location dimension decides the end play of everything the ring retains.
Dimension the groove from the shoulder or face that locates the stack, to the groove wall the ring bears against, not to the groove centerline and not from the shaft end. A chain of dimensions from the end of the shaft adds the overall-length tolerance into the end play for no reason. Baseline dimensioning from the functional shoulder keeps the stack short.
Work the end play out explicitly. Axial play in the retained assembly is the distance from the locating shoulder to the loaded groove wall, minus the stack of parts between them, minus the ring thickness. The groove width clearance does not add to it as long as the ring is loaded against one wall; it only matters when the load can reverse. If the stack of a bearing width and a spacer leaves too much play at worst case, the usual fixes are a tighter tolerance on that one location dimension, a selective-fit shim, or a wave washer, not a tighter groove width. The fits guide covers how to tolerance the bearing seat itself.
Leave the remaining groove features at their standard grades. A width called to the H13 grade per DIN 471 is an easy turned feature; calling it tighter adds gauging time and buys nothing, because the H13 width already clears the ring thickness and its tolerance.
How do inch-series rings differ from DIN 471 and DIN 472 grooves?
Inch tapered-section rings are covered by ASME B18.27, which defines its own ring types and groove tables in inch units. Metric and inch grooves for nearly the same shaft size are not interchangeable, so the drawing must name the ring standard and type, not just the shaft diameter.
The ASME standard covers external, internal and E-ring types, among others, and lists recommended groove dimensions for each ring (ASME B18.27). E-rings deserve a separate note: they install radially, bear on only part of the circumference and carry much lower thrust than a full axially installed ring, so do not swap one for the other on the same shaft without rechecking the load.
Many US drawings call out a ring by a catalog part number and leave the groove to “per ring manufacturer.” That works only if the supplier has the same catalog revision. On a print going overseas, put the groove diameter, width, tolerances and minimum edge margin on the drawing itself, and keep the ring part number as a reference note.
What are the common retaining ring groove mistakes on turned parts?
The repeat offenders are a groove too close to the end, a burr or chamfer on the loaded groove edge, a plating callout that ignores the groove, and a groove placed across a thread or a ground diameter. All of them pass a quick drawing review and show up in assembly.
Burr or break on the loaded edge. A blanket “break all sharp edges” note applied to the groove rounds the very corner the ring must bear on. Exclude the loaded groove edge from the note or call it “sharp, burr-free”; the edge break guide shows how to word an exception.
Plating that is not accounted for. Zinc plating adds thickness to every surface it reaches, including both groove walls; the minimum-thickness classes per ASTM B633 run from 5 to 25 µm. On a 1.3 mm groove for a 1.2 mm ring per DIN 471, a heavy class takes a real share of the 0.1 mm nominal width clearance, and it grows a shaft groove diameter by twice the coating thickness against a tolerance of 0.11 to 0.25 mm in the rows above. State whether groove dimensions apply before or after plating. Rings themselves are hardened spring steel, so plating the ring raises the hydrogen embrittlement question covered in the embrittlement baking guide.
Groove on top of other features. A groove cut through a thread, a knurl or a cross hole loses part of its loaded wall. Keep it on a plain diameter with a full circumferential wall.
Unequal walls on thin sleeves. On a bore groove in a thin-walled housing, the groove depth reduces the wall to a fraction of its nominal thickness. Check the remaining wall under the groove as carefully as the edge margin.
How should the groove be called out on the drawing and RFQ?
Give the groove its own detail view with diameter, width, bottom radius, loaded-wall location from the functional shoulder and minimum edge margin, plus a note naming the ring standard and size. Then say on the RFQ whether the groove dimensions apply before or after finishing.
A workable callout for a 20 mm shaft per DIN 471 reads: groove diameter 19.0 with the standard’s h-tolerance, width 1.30 H13, bottom radius small and blended, loaded wall located from datum shoulder B, minimum material to shaft end 1.5 mm, loaded groove edge sharp and burr-free, ring DIN 471 – 20 x 1.2 (reference). The RFQ should add the shaft material and condition, the finish, whether the finish covers the groove, and whether the ring is to be supplied or installed.
Grooves and chamfers are routine features on the CNC turning line at our lead CNC plant, which runs shafts, bushings and inserts from bar and tube on CNC lathes. A groove toleranced to its ring standard is not a demanding feature there; what matters more is that the drawing says which wall to measure from. Zinc plating or RoHS-compliant trivalent chromate can be applied to turned shafts by a partner plant we manage through surface finishing, with the quote naming where it is done, and the first-article report measures every toleranced dimension on the drawing, groove included, as described on the quality page. For bore grooves in die-cast housings, the bore is finished on the CNC milling line.
For the rest of the package, the machining RFQ guide lists what else to send with the drawing.
Frequently asked
Can a metric DIN 471 ring go in a groove cut for an inch ring?
Not reliably. The groove diameters, widths and ring thicknesses come from different tables, so even where the shaft sizes are close the ring will either sit loose or fail to seat. Choose one system, name it on the drawing, and cut the groove from that table.
Should the groove bottom have a radius?
Yes, a small one, because a sharp internal corner at the groove root is a stress raiser on a rotating shaft. Keep it small enough that the ring still seats fully against the loaded wall (the ring maker’s groove drawing gives the limit), and keep the groove opening on the loaded side square.
How is a retaining ring groove inspected?
Groove width is commonly checked with go/no-go plug or blade gauges, groove diameter with a blade or groove micrometer, and the wall location with a height gauge or optical method from the datum shoulder. The simplest functional check is that a ring from the production lot snaps in fully and cannot be rotated out by hand.
Does a heavy-type ring need a different groove?
Yes, at least in width. Heavy-type rings in DIN 471 and DIN 472 are thicker for higher ring capacity, so take every groove value from the heavy-type table rather than the normal one. A thicker ring does nothing for a groove wall that yields; if the groove is the limit, add edge margin or use a stronger shaft material instead.
Is the edge margin measured from the groove wall or the groove center?
From the loaded groove wall to the end face of the part, which is the solid material that resists the ring. Any end chamfer reduces that margin at the outside diameter, so check it at the chamfer, not at the face.
Sources
- DIN 471: Retaining rings for shafts, normal type and heavy type, DIN Media, edition 2011-04 (listed as replaced by 2026-05)
- DIN 472: Retaining rings for bores, normal type and heavy type, DIN Media, edition 2017-06 (listed as replaced by 2026-05)
- ASME B18.27: Tapered and Reduced Cross Section Retaining Rings (Inch Series), ASME, 1998 (stabilized 2022)
- ASTM B633: Electrodeposited Coatings of Zinc on Iron and Steel, ASTM International, 2023