A detachable cutting tool capture for a cutting block provides a guide surface to convert an open surface block into a slotted block for plying a surgical cutting tool along the surfaces of the guide during a surgical procedure such as a bone resection with a blade. A magnetized catch provides a convenient device for securing the capture and the block together. A triangular cam on the detachable capture in conjunction with a “v” groove in a magnetized lever of the catch permits a pin of the catch to be selectively retracted from or extended into an aperture of the block when the lever is rotated so that when the pin extends, it serves to secure the combined apparatus for cutting. Mating surfaces of the block and capture provide additional structure for supporting the capture with the block to secure them from relative movement.