What is the difference between the model number CMHT77620 and CMHT77621? Wilson October 03, 2020 20:00 The unit CMHT77620 should have a hole that is open for the pencil to slide through.The cmht77621 that is meant to stay attached to the unit as a marking pin you use to push into the drywall to make a mark. Please see attached pictures. Related articles What is the part numbers and sizes for the Craftsman trimmer line? Craftsman CMHT77637 Laser Distance Measure Manual Comments 0 comments Please sign in to leave a comment.