A watch strap has a connection at the watch and another at the buckle. A width that matches the first connection may differ from the width needed at the second. Recording both ends, together with the fastening system, helps turn a vague “Will it fit?” into a question a supplier can answer.
Measure the gap at the watch
For a conventional attachment between two lugs, measure the clear distance between their inner faces at the strap connection. The HIRSCH size guide illustrates the distinction between that gap and the wider measurement across the outside of the lugs. Case diameter is a different dimension.
Start with the watch maker’s specification for the exact reference. If measuring an accessible gap, record the tool, position and unit. An unclear or fractional reading is a reason to seek clarification, rather than round it into a preferred catalogue size.
Delugs’ lug-width guide notes that integrated or special attachments need a separate compatibility check. Record the end shape and attachment hardware alongside the width; ask about the exact combination when these remain unclear.
Read both numbers in a tapered width
In the Delugs convention, 20–16 means 20 mm at the watch and 16 mm at the buckle. The difference describes the narrowing between the ends. The second number is not a length. Check another seller’s labels before applying this convention to its listings.
If retaining a buckle, the same guide measures its inside gap at the spring-bar connection, or the width of the strap end already fitted there. Measuring across the outside of the metal frame would include material that the strap does not occupy.
Use the following record to keep the dimensions tied to their locations:
| Record | Where it belongs | What it does not establish |
|---|---|---|
| Watch attachment width | The strap connection between the inner lug faces. | Case diameter, end shape or attachment-hardware compatibility. |
| Buckle attachment width | The strap end and inside connection of the selected buckle. | The outside size of the frame or a folding clasp’s full requirements. |
| Finished strap thickness | The particular part that enters or fastens within the clasp. | The thickness of another part of the strap. |
| Strap length | The maker’s stated long and short sections and sizing method. | Either attachment width. |
Check the clasp’s additional requirements
Width is one requirement among several. HIRSCH’s Pusher Buckle, BC1024-1 specifies a maximum strap thickness of 3.7 mm on the hole side. That limit belongs to this product; it is not a standard allowance for every folding clasp.
A different example appears in Delugs’ Spring Deployant Clasp customization note. For the buckle substitution described there, the maker specifies a 16 mm buckle and a tongue of 2 mm or less. This is a condition for that particular conversion, not permission to interchange all buckles with the same width.
Ask the supplier to confirm the fastening arrangement as well as its dimensions. Keep the stated thickness limit attached to the correct strap section. The guide to leather thickness and the finished assembly explains why a material specification cannot replace a measurement of the completed part.
Prepare a fit request before changing parts
This editorial checklist is a record for a supplier or watchmaker, rather than a fitting procedure:
- Identify the exact watch reference and photograph the existing attachment without dismantling it simply to obtain a photograph.
- Record the watch-end width and buckle-end width separately, with the source or measurement location for each.
- Name the buckle or clasp you intend to retain. Add its documented attachment method, thickness limit and any tongue or opening requirements.
- Send the strap model, length option and unresolved details together. Ask for confirmation of the complete combination before altering or fitting parts.
Wrist sizing remains a separate choice. Matching the two attachment widths does not establish a comfortable strap length. Likewise, material selection needs its own record; see watch-strap uppers, linings and finishes.
Sources and scope
The manufacturer references above explain measurement locations and specific hardware conditions. No strap, clasp or watch was physically tested for this article, and no replacement fit is certified. These examples do not establish the construction of any historical Möhel accessory. Browse the practical guides directory for related material and storage notes.