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1.5mm Diameter EXPANDABLE Straight Spring Bars: 16-21mm (1 Pair)
Straight spring-loaded watch pins to fit strap fittings between 16mm and 21mm. Sold as a pack of 2 spring bars.
The size of the spring bar required to fit your watch strap will be the same size as the width of the part of the watch strap which connects to the watch case. See the diagram below: