The Beansprout straps by Aaron Keim have no metal parts and are my favorite. https://www.thebeansprout.com/store/beansprout-banjo-and-ukulele-strap
My second choice is this one from GoldTone, which also fortunately lacks any parts that would scratch. https://goldtonemusicgroup.com/goldtone/accessories/cs.
My second choice is this one from GoldTone, which also fortunately lacks any parts that would scratch. https://goldtonemusicgroup.com/goldtone/accessories/cs.