The DNR reg says 5 in spread minimum to keep. I know traps are made with culling rings, but I haven't read anything about a requirement for them. If I pull the trap and they don't meet the required size they get thrown back in! I also made a bait tray to keep it out of the dirt/silt.
Two unobstructed
escapement rings (23/8 inch inside
diameter) must be installed on an
outside vertical wall. Each trap must
be marked with a fluorescent green or
lime green float bearing the owner's
name and address in one-inch letters
Thats straight from the regs. they now require the escape rings.