A custom sapphire watch crystal is defined by six things: outer diameter, thickness, edge and chamfer, profile (flat, domed or box), any anti-reflective coating, and the inspection criteria you will accept it against. If you can put those six on a drawing or a dimension sheet, a supplier can review the part and start a real conversation. If any of the six is missing, the first round of quoting turns into guesswork, and the sample you get back may not match what your case actually needs.
This guide walks through what to put on the drawing before you ask for a quote, so the review is based on your geometry rather than on assumptions.
Start from the case, not the crystal
The crystal has to seat in your case and hold a gasket. Before specifying the glass itself, confirm the seat diameter, the gasket groove, and the height budget between the dial and the case top. The crystal's outer diameter and thickness are constrained by those numbers, so it is worth fixing the case interface first and letting the crystal dimensions follow.
If you are replacing a crystal in an existing case, measure the old part and the seat directly rather than copying a catalogue number, because two crystals with the same nominal diameter can differ at the edge in ways that change the fit.
The six things a drawing should carry
| Specification | What to state | Why it matters |
|---|---|---|
| Outer diameter | Nominal diameter and the fit you need (press fit, gasket fit, or bezel-retained) | Determines whether the crystal seats and seals correctly in your case |
| Thickness | Overall thickness, and profile height if domed or box-type | Affects height budget, strength and how the profile reads on the wrist |
| Profile | Flat, single-domed, double-domed, or box-type | Changes optics, case height and the tooling used to make it |
| Edge and chamfer | Edge finish and any chamfer or bevel dimension | Controls fit against the gasket and the risk of edge chipping in assembly |
| Coating | Anti-reflective coating, one side or both, or none | Changes glare, appearance and inspection expectations |
| Inspection basis | The dimensions, clarity and surface criteria you will accept against | Lets both sides agree on what "good" means before a sample ships |
You do not need every value finalised to start. A dimension sheet with your target ranges and the tolerances you care about is enough for a first engineering review.
Tolerances: say which ones matter
Not every dimension needs a tight tolerance, and asking for tight tolerances everywhere adds cost and rejects without improving fit. The dimensions that usually matter most are the ones that control seating and sealing — outer diameter and the edge geometry against the gasket. Call those out specifically and let the less critical dimensions carry a normal working tolerance.
If you are not sure which tolerances your case can live with, that is itself a good thing to raise in the review rather than to guess at.
Coating and profile are design decisions, not afterthoughts
Whether a crystal is flat or domed, and whether it carries anti-reflective coating on one side or both, changes how the watch looks and how it should be inspected. These are worth deciding early because they affect tooling and the sample you will evaluate. Two companion articles go deeper: one on single-domed versus double-domed profiles, and one on single-side versus double-side AR coating.
Frequently asked questions
Do I need a full technical drawing, or is a dimension sheet enough?
A dimension sheet with outer diameter, thickness, profile, edge and any coating requirement is enough to begin a project-specific review. A full drawing helps once the geometry is settled.
Can I specify a crystal by referencing an existing watch model?
A reference model can communicate the look you want, but the review still needs your own case dimensions, because seat and gasket details vary between cases.
What if I only know the look I want, not the numbers?
Then start from the case interface. Confirm the seat and height budget first, and the crystal dimensions can be worked out from there during the review.
Next step
If you have a case or a target geometry in mind, submit a drawing or dimension sheet for a project-specific review. Include the six items above where you can, and flag anything you are still deciding — the review is more useful when it can work from your actual constraints.
To discuss your custom sapphire watch crystal requirements with an experienced team.