It's 1 1/4" wide slit. Basically we sliced the entire vertical slab and pulled the lower part forward to create the opening. This was a very meticulous client who knew every knife, every handle, their thickness and their use. He said he would never consider rubbing the edge on the stone so we didn't add any additional protection either for the edge of the blade or for this very durable stone. This doesn't work with every type of material but it certainly works with granite.