A gearbox is stripped on the bench, and a circlip is lying in the parts tray with no packet and no drawing. Before you can reorder it you need its designation. Here is the three-step method our customers use, based on two calliper measurements and the standard dimension tables.
Step 1: External or Internal?
Look at the lugs - the two ears with plier holes at the gap:
- Lugs protrude outward beyond the ring body → external circlip (DIN 471). It expands over a shaft, so the pliers need leverage from outside.
- Lugs point inward toward the centre → internal circlip (DIN 472). It compresses into a bore.
If it has no lug holes at all and slides on sideways, it is an E-clip or wire C-clip - a different family (DIN 6799).
Step 2: Take Two Measurements
- Thickness (s): measure the flat, axial thickness of the ring with callipers or a micrometer. Standard values step through 0.4, 0.6, 0.7, 0.8, 1.0, 1.2, 1.5, 1.75, 2.0, 2.5, 3.0, 4.0 and 5.0 mm - your reading should sit very close to one of these.
- Free diameter (d₃): with the ring loose and unstressed, measure the inner diameter of an external ring, or the outer diameter of an internal ring. Measure across the middle of the ring, away from the gap, and take a couple of readings.
Key concept: the free diameter is deliberately offset from the groove it fits - smaller for external rings, larger for internal rings - so the installed ring grips under spring tension. This offset makes the free diameter a fingerprint for the nominal size.
Step 3: Match It in the Chart
Open the matching dimension chart and find the row where both your measurements agree:
- External ring → DIN 471 size chart (Free I.D. d₃ column)
- Internal ring → DIN 472 size chart (Free O.D. d₃ column)
The nominal size in that row is the shaft or bore diameter - and that is the size you order.
Worked Example
- The mystery ring has outward-pointing lugs → external, DIN 471.
- Callipers read: thickness ≈ 1.2 mm, free inner diameter ≈ 23.2 mm.
- In the DIN 471 chart, the row with s = 1.2 and d₃ = 23.2 is nominal Ø25.
Order: DIN 471-25 (external circlip for a 25 mm shaft). Note the ring itself never measures 25 mm anywhere - the nominal size lives on the shaft, not the ring.
If Nothing Matches
- Close but consistently off? You may be holding an inch-series (ANSI) or JIS ring - common in imported equipment.
- Free diameter reads near the groove size? The ring has probably been overstretched in a previous removal and lost its spring set. Do not refit it - a sprung ring cannot grip reliably. Measure the groove instead and order new.
- Still stuck? Send us the two measurements on WhatsApp - identifying rings is our day job.
Found Your Size?
Every DIN 471 and DIN 472 chart size stocked in spring steel and stainless, ex-Mumbai with same-week dispatch.
View Circlip RangeFrequently Asked Questions
How do I tell an external circlip from an internal one?
Look at the lugs (the ears with the plier holes). On an external circlip they protrude outward beyond the ring body, because the ring must be expanded to fit over a shaft. On an internal circlip the lugs point inward toward the centre, because the ring must be compressed to enter a bore.
What should I measure to identify a circlip?
Two things with callipers: the ring thickness (the flat axial dimension) and the free diameter of the unstressed ring - inner diameter for an external ring, outer diameter for an internal ring. Together these two numbers identify the nominal size in the DIN dimension tables.
Why does my circlip measure smaller than its nominal size?
Because the nominal size is the shaft or bore diameter it fits, not a dimension of the ring itself. A DIN 471-25 external circlip has a free inner diameter of about 23.2 mm - smaller than the 23.9 mm groove so the installed ring grips. This offset is exactly why the free-diameter column in a dimension chart identifies the ring.
What if my measurements do not match the DIN chart?
The ring may be an inch-series (ANSI/military) or JIS ring, a non-standard heavy-duty pattern, or simply a used ring that has been overstretched and lost its shape - a sprung ring should be replaced, not reused. Send us the thickness and free diameter and we will identify it or supply the correct replacement.