Just finished making a couple of strops - one for me and one for my knife-making mate. I used "scrap" leather off the ends of a couple of belts that I made (I'll post these once I've taken the pics) and some oak I had lying around after I made SWMBO a coffee table. The hangy uppy bits are 2mm round thong.
The leather bits are about 8" long - the same as my sharpening stones. (I've used the black one - hence the marks!)

The leather bits are about 8" long - the same as my sharpening stones. (I've used the black one - hence the marks!)