these also work
https://www.amazon.co.uk/EventClip-BibClips-running-cycling-numbers/dp/B00GY6A9J6/ref=sr_1_9?crid=2XRKZ1OSLFX6W&keywords=race+number+clips&qid=1644237871&sprefix=race+number+clips%2Caps%2C56&sr=8-9
I had been looking at those, it seems easier than a belt if they work.
+1 for event clips
@Airhead started
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these also work
https://www.amazon.co.uk/EventClip-BibClips-running-cycling-numbers/dp/B00GY6A9J6/ref=sr_1_9?crid=2XRKZ1OSLFX6W&keywords=race+number+clips&qid=1644237871&sprefix=race+number+clips%2Caps%2C56&sr=8-9