You have several options. PML makes a retainer using three threaded inserts and a metal retainer that fits over the rear enclosure. They are about $15. Giant leap sells a Slim line retainer that is epoxied to the motor mount tube and uses a snap ring to hold the motor in place - ~ $20. Another option is to build your own similar to the "tang" , but uses two or three inserts and the same number of tangs to retain the motor. There are other manufacturers of retainers similar to the slim line. All work great. The only issue with those is in the event of a hard landing on the retainer that may bend it and prevent or make it hard to get the casing out. Aeropack makes a great retainer, but I dont know if they make one for 29mm motors.

Yes, Aeropacks are made for 29mm, and they would be my retainer of choice. Alternatively, the threaded slimline is a great choice, or one could go with the simple Kaplow Clips. Friction fitting is still an option as well, though not as common.

Also remember, for most of us, the number of rockets on hand can be rather large. The clip method is cheap, and I have never had a failure when 2 clips were used. I use them on 18,24, and 29mm motors. For those "special" projects my first pick is Aero Pack. For smaller rockets the motor tube is the heart of the rocket. The front holds the kevlar for recovery, the aft holds the motor. The fun part is how you want to put them together. This is where walking up and down the flight line can pay off. Almost everyone will show you how they do it, and there are some sharp guys out there. Now if it would just rain......... 8)

My second failure going for L1 was not using sound positive retention. My motor ejection shot the motor casing past a steel hook! From that point on, for myself and anyone I'm up for certifying, you'd better have sound retention. The casing landed within a 100 feet of Nadine, and I'll never do that again. Aero Pack is great for larger rockets, but I used GLR's Slimline for my L1 & L2, and I've never had a failure, and don't expect to. I use it currently on three, "safe" rockets. Highest recommendation. 8)

Personally, I'll always use motor retention if possible -- and there are a lot of wonderful systems out there. Aeropack's is wonderful, G-Leap systems are great, etc. That said, I have friction fit perhaps 40 of my last 50 flights, largely due to the fact that I tend to fly minimum diameter birds. I've lost just one casing over the years (I'm also oft-accused of overdoing my charges, so that makes motor retention all the more critical!)

Friction fitting works great. I do have a major advantage, though-- if I have to pound a motor out, I don't have to worry about dis-lodging centering rings, as I almost never use centering rings.

Bottom line, friction fitting is fine. I have *never* had a casing move a small amount, other than my kicked casing. Many of you saw my rocket "BoB" make dozens of flights over the years. Every time, that was a friction fit casing with flimsy centering rings....