are specially made of tough, 4140 alloy steel for this application. Click here for more details. Slip-ON Quill Nuts Unique design for machinery stops Speed up set up and production. No... retrofit required. Just slip on and you are ready. Can be used in conjunction with existing quill nuts. Ideal for milling and all types of machinery that require adjustable stops.... Quill stops made of 6061 T6 aircraft aluminum. Current size of machinery adjustable stops - 1/2" - 20. Other sizes available. Copyright 2003 -by Slip-On Lock Nut Co., Inc...