Watch Case Back O-Ring Gasket Classic Pack 24 To 29mm

Vintage and dress watches carry history on their dials, but their gaskets don’t last forever. The Classic Pack is an 18-piece O-ring case back gasket assortment covering six essential mid-small sizes 24mm, 25mm, 26mm, 27mm, 28mm, and 29mm with 3 gaskets per size at a consistent 0.6mm thickness.

This size range is the sweet spot for classic watches. Older Seikos, vintage Omegas, slim dress watches, and many European timepieces. If you work on or collect watches from this era, The Classic is a pack you will reach for repeatedly.

Over time, rubber gaskets dry out, lose flexibility, and fail to seal properly. Once that happens, humidity and moisture enter the case, threatening the movement inside. However, replacing the gasket during a routine battery change takes only a few minutes and prevents far more expensive damage down the line.

Specification

• Sizes Included: 24mm, 25mm, 26mm, 27mm, 28mm, 29mm
• Quantity: 3 of each size
• Total – 18 Gaskets
• 0.6mm thickness

Using these gaskets is straightforward. First, open the case back carefully. Next, remove the old gasket and clean the groove. Then, select the closest matching size from the pack, apply a small amount of silicone grease, seat it in the groove, and close the case back.

The Classic Pack is designed for watchmakers, collectors, and hobbyists who regularly work on mid-century and vintage timepieces. With 3 gaskets per size, it provides enough stock to handle repeat servicing, restorations, or personal projects without the need for constant reordering.

Measurement Guide

If you still have the old O-ring, even if it is stretched or broken, you can use it as a reference. Measure the Thickness, Use a digital caliper to measure the “cross-section” (thickness) of the rubber. Measure the Internal Diameter (ID): Lay the gasket flat on a surface without stretching it. Measure across the inside of the circle from one inner edge to the other.

If the watch is missing its O-ring entirely, you must measure the watch case itself to find the correct fit. Measure the Case Groove, locate the circular track (groove) where the gasket sits inside the watch case. Use a digital caliper to measure the Inside Diameter of that groove.

Stop hunting for individual sizes. Keep the most common mid-small seals on hand and ready to go. Add The O-Ring Gasket Classic to your workbench today