The inner diameter decides whether a ring goes on, stays on, or falls off. Too small and the ring will not seat, or it creases at the inner cut. Too large and it shifts under the strap and leaves the rim it was bought to protect. There is no universal clearance: the right figure comes from the product, the wrap and how the ring is fitted.
Measuring the diameter you actually have
Measure the product across three diameters at right angles and take the largest and smallest. Coils and rolls are oval by a millimetre or two, and a ring that ignores that will be tight on one axis.
State what the ring has to pass over. If it goes on before the wrap, it fits the bare product; if it goes on outside a film wrap, add the wrap thickness to the diameter.
Specification at a glance
The table shows how the inner diameter is derived for the common fitting situations.
| Fitting | Inner diameter | Note |
|---|
| Bare product, push fit | Measured OD plus small clearance | Seats by hand |
| Over a film wrap | OD plus wrap thickness | Add both sides |
| Held by strapping | OD plus clearance | Ring wide enough to stay under the strap |
| Stepped product | Largest section it passes | Not the seating diameter |
| Oval product | Between the two readings | Check the fit on the item |
Clearance, fit and the strap
A push fit needs just enough clearance to seat by hand. A loose ring relies on the strap to hold it, which works only if the strap crosses the ring and the ring is wide enough not to slip out from under it.
Where the ring sits on a tapered or stepped product, the inner diameter should be set to the largest section it has to pass, not to the seating diameter.
Why this goes wrong in production
The most common error is quoting a nominal product size from a catalogue rather than measuring the goods. A coil described as 1,500 mm is rarely exactly 1,500 mm, and the ring is cut to the number that was written down.
The second is forgetting the wrap. A ring cut for the bare coil will not go over the coil plus film without being forced, and forcing it creases the inner edge.
Questions buyers ask before ordering
How much clearance does a ring need?
Just enough to seat by hand. More than that and it shifts under the strap.
Do I add the wrap thickness?
Yes, if the ring goes on outside the film wrap.
What if my coil is oval?
Give both readings and check the first ring on the coil.
Can I order by nominal size?
It is the main cause of a remake. Measure the goods.
Can the inner diameter be adjusted after cutting?
No. The inner cut is made to size, so the measurement has to be right first.
Share the drawing or a product sample with mona@hengnicepacking.com and we will confirm feasibility before quoting.
