Mine are 36" deep. Got 'em from a building I used to work in when we "upgraded" the maintenance shop.
The property manager said
"throw 'em in the garbage bin" to make room for the new shelving.

So much for "recycling".
My supervisor wrote me a receipt for $5 to show anyone I didn't steal 'em if anyone saw me loading them into my truck. I used 3/4" plywood too.