Usaully it's 2 inches tall with a drilled hole at the top of it so the slit doesn't crack and keep going up the bar.. not sure about the width of the slit
If you cut 2 slits, with something like a hacksaw, it will work but it won't be strong. If you have one slit, you want the slit to be somewhere around a quarter of an inch wide... That should do the trick.
you drill a hole where the slit should end like an inch and a half to 2 inches up your bars and then you cut 2 slits right next to eachother so that it's wide enough and when you clamp it it doesn't just clamp together.