They are an integrated part of every technique. For example We have a very small statured Japanese female Yudansha. When she takes Ukemi from you wondering how the heck she is going to control and pin you with her tiny hands...
In a word. Fingers!
Ouch!!! Well that be two words... but her use of an Uke's fingers is just as good as any technique I've experianced so it hard for me not to think of finger "locks" and ouch!!! in the same breath. LOL