I DEFINITELY do the exact same thing. It's definitely not uncommon!
When I didn't have access to razors anymore I would scratch and bite myself and such desperate to leave a mark because I missed what I used to do. So I totally get it <3
In response to what Tig said - I don't specifically find things like stress balls to be any type of magical cure... It's really hard to think about anything other than hurting yourself when you want to. I find that the thing that most effectively stops me from hurting myself is placing myself around other people. I never WANT to be around other people at this time, and it doesn't make me FEEL any better, but it effectively stops me from hurting myself, you know? And then you get the initial thought out of your mind and it calms you down.
But I guess things like stress balls do work for some people. I just know it doesn't actually work for everyone especially when they're so consumed with self harming thoughts.