Walk through on the process. Used my Precision Matthews TL 1640 lathe including the 22J collet system and Sjogren Speed Chuck as well as the Bridgeport. Starting with a 12" x 2-1/4" 6061 Aluminum round bar (thru hole on the lathe is 2.550") in the 3 jaw chuck, I drilled and bored a 3/4" thru hole then a 1" diameter deep counterbore to create the inside step. The O.D. was reduced an inch to 1-1/4". Then it was parted and flipped for facing using the 22J collet system. The work then moved to mill where strategic flats were added to assist the clocking of the locking and slot features. When I did the locking features I used a 3/16" long center drill and drilled all the way through the part. On the first side, I finished the feature with a 3/16" end mill just by plunging full depth. Another option would be to rotate the part during the cut which makes the process considerably more complicated. Then I flipped the part and confirmed that it was properly positioned by ensuring the end mill went into that existing hole. Then repeated the process. Last step was rotation to the third position and making the slot. The thicker area I used the plunging technique to quickly chunk out the excess. Then, I machined the slot from the finished end towards the large end. Finish cut was an extra +/- 0.001".