These can be used on Cat 50 machines, you need to Use a longer and different thread Draw-Bar, and or Get a special Retention Knob to go on these NMTB 50 to work as Cat 50. Do some Googling to figure out the simplest method. If somebody finds a great article with the best info on that?? Please message me with a link, and I will ad that to this ad.The item "NMTB 50 shell mill holder 2 arbor pilot taper tool precision cat 50 choose 1" is in sale since Sunday, April 28, 2019. This item is in the category "eBay Motors\Parts & Accessories\Wholesale Lots\Tools". The seller is "dragar85" and is located in Minneapolis, Minnesota. This item can be shipped to United States, Canada, United Kingdom, Denmark, Romania, Slovakia, Bulgaria, Czech republic, Finland, Hungary, Latvia, Lithuania, Malta, Estonia, Australia, Greece, Portugal, Cyprus, Slovenia, Japan, China, Sweden, Taiwan, Thailand, Belgium, France, Hong Kong, Ireland, Netherlands, Poland, Spain, Italy, Germany, Austria, Bahamas, Mexico, New Zealand, Philippines, Singapore, Switzerland, Norway, Saudi arabia, Ukraine, United arab emirates, Qatar, Kuwait, Bahrain, Croatia, Malaysia, Chile, Colombia, Costa rica, Dominican republic, Panama, Trinidad and tobago, Guatemala, El salvador, Honduras, Jamaica.