Here is a vintage set of Production Stops components for a C&H mat cutter that has a bar diameter of one half an inch. I have other C&H Mat Cutters with 5/8' bars and these do not fit on them! I had these for an older version Model CH 40 (or 48 or 60)...I don't remember the exact model...but one of them. The base got wet and deteriorated so I tore it down and kept these parts for years.
They will make a great addition to your mat cutter if you have the correct one!
Note: The slide block (cutting head) is probably an original design (or at least a very early design) and is a bit different than the style designed and supplied on more recent machines. There are typically two blade holders on the slide block...the bevel side holder (used for cutting the bevel of a mat opening) and the straight side holder (used for cutting boards to size). This slide block only has the bevel side holder!