Snap Shackles

https://marinestore.co.uk/PBSM-1106.html Nice brass ones

http://www.osculati.com/it/cat/Scheda.aspx?id=590
http://www.behejsepsem.cz/shop/15-vypousteci-karabina
http://www.k9trailtime.com/shop/quick-release-clip.html
http://www.dogathlon.es/en/carabiners-snap-hooks/169-canicross-quick-release-carabiner