A specialised tool from HIRSCH which enables you to notch perfect cut-outs at the outside edges of the watch end of straps to make them fit a smaller watch, whilst retaining the spring bar loop.
Doing this to a strap will give it a bulkier appearance on the watch.
For example you could fit a 24mm watch strap to a 20mm watch by cutting the strap down by 2mm at each end.