How to change a Seiko strap

This is the cheapest meaningful change you can make to a watch, and the reason it is worth a page of its own is the failure mode: a slipped spring bar tool leaves a bright scratch on the inside face of the lug, in the one spot on the case that is impossible to hide and costs more to correct than every strap you will ever own. The procedure that avoids it is not difficult. It is just specific.

Step 1 — find your lug width before you buy anything

Lug width is the distance between the two lugs, which is also the width of the strap end that fits there. It has nothing to do with case diameter — the 45 mm Prospex Sumo takes a 20 mm strap and the 42.5 mm Seiko 5 Sports takes 22 mm, which catches people out constantly. Measure across the gap with a ruler or calipers, or look the reference up: the lug-width guide lists this registry by measurement. Seiko does not publish a lug width for every reference, and where it does not, measuring is the only honest answer.

Step 2 — set up so a slip cannot reach the case

• ·Fold a cloth or a tea towel and put the watch face-down on it. A microfiber cloth over a hard surface is ideal. This protects the crystal and stops the watch sliding while you push.
• ·Work on one strap end at a time. Removing both before fitting either is how spring bars get lost and mixed up.
• ·Use the forked end of the tool, not the pin end. The fork straddles the spring bar and compresses it. The pin end is for push-pin bracelets and drilled lugs, and it is the end that slips on a lug face.

Step 3 — the removal

Slide the fork into the gap between the strap end and the lug, locate the shoulder of the spring bar, and press it toward the middle of the case— parallel to the strap, never levering upward. The bar compresses, that end clears the lug hole, and the strap drops free with gentle pressure outward. If it will not go, you are on the wrong part of the bar, not using too little force. Keep the spring bars; they are matched to the width and they are the part nobody has a spare of.

If your Seiko has drilled lugs— visible holes through the outside of the lug — this is much easier. Push the pin end of the tool straight into the hole from the outside, the bar compresses, and nothing goes near the inside lug face at all. If you are choosing between two references and you change straps often, drilled lugs are a real advantage.

Step 4 — fitting the new strap

Thread the bar through the new strap’s end loop, seat one tip in its lug hole, then compress the other tip with the fork and walk it into place. You should feel and usually hear it seat. Then test it before you wear it: hold the watch head and pull the strap firmly away from the case. A bar that is not seated will come out there, on your desk, rather than on a street. Do that on both ends every single time.

What changes between the strap types

• ·Straight-end straps fit anything of the right width. They leave a visible crescent of daylight between the strap and a curved diver case. That gap bothers some people and not others; it is cosmetic, not a fault. Seiko’s own 22 mm diver’s urethane strap is a straight end.
• ·Curved-end straps are cut for a specific case. They close the gap completely and they are not interchangeable — a curved end cut for a Turtle will not sit properly on a different case. Confirm your reference before buying one, because “22 mm” is not enough information on a curved end.
• ·A NATO adds height. The strap passes underneath the case back, so the watch sits a few millimeters higher on the wrist and wears taller. On an already thick diver that is noticeable. The compensation is that a NATO needs no sizing, fits any wrist out of the box, and is the only strap type that keeps the watch on your arm if one spring bar fails.
• ·Quick-release spring bars are worth seeking out. They have a small lever on the bar itself and need no tool at all. Many aftermarket straps now ship with them; Seiko’s factory bars generally do not.

Two things this page is not

It is not bracelet resizing. Taking links out of a steel bracelet is a different job with a different tool end, and that has its own page— keep the links you remove, in the box, because they are the item that becomes unobtainable later and the one a future buyer asks for.

And it is not a shopping list. If what you actually need is to choose a strap rather than fit one, the strap and bracelet roundup ranks the options by width and material, and the bracelet replacements page covers the solid-link upgrades. The four items below are the minimum kit: the tool, a nylon strap that fits any wrist, the factory-correct Seiko urethane, and a curved-end rubber for a diver case.