I have a couple of those commercial sanding blogs with the spring clump front and back, but to me those things are big, flat only and don't hold the sand paper firmly and stretched, so it's easily tear out.
I needed I sanding blog that will do few things for me:
1) I wanted it to be smaller and fit nicely in my palm.
2) To hold the sand paper tightly without moving.
3) To be able to sand in tight and big round over corners
4) Easy to change sand papers.
Step 1: The Blog
Also they are just flat... I can use my power sanders for just flat sanding.
So I come up with a way to feed the paper front to back with the help of some grooves in the body and tongues on the handle.
This way my sand paper fits very tight on my block.