The right strap is chosen with three measurements and one question. The measurements are the lug width in millimetres, the length of the two sides, and the thickness that passes under the lugs. The question is where you will wear the watch: on the wrist every day, in water, under a shirt. The rest, colour and leather included, comes after.
What is the lug width of my watch?
The lug width is the distance between the two lugs of the case, measured on the inside. It is read in millimetres and allows no approximation: a 20 mm strap on a 21 mm lug wobbles, a 22 mm one does not fit. The most common measurements are 18, 19, 20, 21, 22 and 24 mm. The 19 and the 21 exist more often than you'd think: old Omegas, many Tudors, the Rolex Air-King. If you don't have a calliper, look up your watch's reference in our measurements archive: the measurement is the one taken at the bench, not the one stated by the catalogue.
Be careful with integrated bracelets. A Royal Oak, a Nautilus, an Oyster with a link bracelet designed for that case do not have a lug in the usual sense: there, the strap is made to measure or not fitted at all. In the archive, these entries deliberately do not report the measurement.
How long should a strap be for my wrist?
A standard strap measures 115 mm on the long side and 75 mm on the short side, with seven holes at 7 mm spacing. It suits wrists between 16 and 19 cm. Below 16 cm you need the short length, above 19 the long one. It isn't a minor detail: a strap that's too long lets the tail come out of the second keeper, one too short closes on the last hole, which is the first to split. Measure your wrist with a tailor's tape, snug but not tight, and tell me the number: I'll work out the right length.
How thick should a strap be?
Thickness is read at two points: at the lug end and at the buckle. A classic calfskin strap starts at 3.5 mm and tapers to 2.5 mm at the closure. Under a low lug, such as that of a Calatrava or an old Seamaster, 4 mm will not fit. On a 44 mm Panerai, 3 mm looks like nothing. The rule I use: the thickness at the lug end must fill the lug without forcing it, and the taper towards the buckle must be visible to the eye.
Which leather, depending on how you wear the watch?
Calfskin. This is the leather I recommend for your first serious strap. Vegetable-tanned calfskin develops a patina within six months, softens on the wrist and holds up to daily wear. In the leather selection you'll find the smooth, the hammered and the vintage finish, which already starts darkened at the edges.
Alligator. Chosen for the case that deserves it, not for the price. The belly cut gives symmetrical, soft scales; the back cut, the hornback, has a bony ridge at the centre and suits larger watches. Every piece comes with a CITES certificate. You can see the scales here.
Shell cordovan. It isn't leather in the usual sense: it's the fibrous layer from the horse's hindquarters, tanned for six months by Horween in Chicago or by Shinki in Japan. It doesn't crack, doesn't crease, and reflects light like no calfskin can. For those who wear the same watch for ten years.
Rubber. For the sea and for summer. Italian vulcanised rubber doesn't absorb sweat and isn't bothered by salt: you rinse it and it's back to how it was. In the rubber selection there are models for Submariner, Seamaster and Aquaracer, with the lug widths they require.
Nylon and fabric. The NATO passes under the case in one piece and won't let the watch fall if a spring bar fails; the two-piece sits more neatly under a cuff. These are straps to change often, for travel, for boating. You'll find them among the military straps.
Tang buckle or deployant: which one?
The tang buckle is the simplest and most reliable system: a steel tongue that passes through the hole. The deployant distributes pressure across the whole length and opens without removing the strap: for those who put it on and take it off ten times a day the difference matters, for those who wear it from morning to night it doesn't. In both cases, the buckle width follows the strap's taper: on a 20/16, the buckle is 16 mm, not 20.
What colour should I choose for the strap?
The strap's colour speaks to the dial and the case metal before it speaks to your shoes. On steel, black, midnight blue and cool browns work well; on yellow gold and bronze, warm browns, cognac, olive green. A white dial accepts almost anything; a black dial copes poorly with light browns. I've written about this at length in the guide to colour matching by dial. The rule of matching shoes and belt applies in front of a suit and stops applying everywhere else.
How long should a well-made strap last?
A calfskin strap worn every day lasts two or three years; rotating it with a second strap, double that. Alligator keeps its structure but loses elasticity after a few years of daily wear. Cordovan lasts as long as the watch. Three precautions are enough: keep it dry, don't leave it on the dashboard in summer sun, feed it with a neutral balm twice a year. The rest is patina, and patina is the beautiful part.
And if my watch isn't in the measurements archive?
Write to me with the reference and a photo of the case seen from above: I'll take the measurement myself. And if the case calls for a strap that doesn't exist on the shelf, whether for the lug shape or the thickness, the made-to-measure work is done in the atelier, in Via XX Settembre in Milan or by video call. It isn't a fad: it's how a strap comes into being when the measurement isn't standard.
What words do you need to order a strap?
Lug width: the lug width, in millimetres, measured between the case's lugs. The strap must match it exactly.
Taper: the strap's taper from the lug end to the buckle, written as 20/16. It changes the buckle and changes the way the strap sits on the wrist.
Belly cut and hornback: the two alligator cuts, from the belly and from the back. The first is smooth and symmetrical, the second has a bony ridge at the centre.
Shell cordovan: the fibrous layer from the horse's hindquarters, vegetable-tanned for six months. Horween and Shinki are the two tanneries that matter.
Spring bar: the spring-loaded bar that fixes the strap to the lugs. It has a diameter, 1.8 mm on most modern Swiss watches and 2 mm on Rolex, and should be chosen with the same care as the strap.