I've used these 2"x7" aluminum sanding block in my shop for years to be able to level and sand out slide and frame flats to any level of polish that my client has ordered. I think they work so well, that I wanted to offer them for sale. The clamp plate keeps the abrasive paper pulled taught, while the finger and thumb grooves on the sides help you control and direct the block without tiring you out, trying to keep the paper taught, like on a makeshift sanding block.
My sanding blocks use a 2" wide piece of sandpaper or 2" wide emory strip. I buy sheet sandpaper in 9"x11" sheet and when I tear it length-wise, I get 3 strips 2" wide, plus another 1" wide strip that I save for general shoe-shine blending.
I include a loose piece of 2" wide 7" long 40 durometer Buna-N rubber that you can use between the abrasive paper and sanding block at your option. If I am sanding out flats that are a little wavy and they have roll marks, I normally use the rubber to allow some give in the sandpaper and help it follow the surface, rather than forcing it to level the surface.
When you've worn out a piece of paper, tear off those un-used ends and save them for wrapping around sanding sticks and files to sand small surfaces.