Making new tail cone for Aeropack Retainer

Hi all,

I'm posting because I could use some help with the Aeropack retainers.

A friend asked if I could make a new aeropack tailcone retainer for a project. No problem!

Well, maybe just a small one. I don't know if anyone on here is a machinist or has an answer straight from the horse's mouth, but I doubt I will get one from Aeropack, considering the information I have on hand from my measurements.

This is a 98mm retainer. It appears that the thread on these retainers might be a modified whitworth thread based on my rough measurements. Whitworth threads have a rounded peak/valley, and have a 55 degree angle. My measurements using calipers (I don't have an optical comparator), combined with calculations derived from said measurements, show that I have approximately 56.2 degree thread. So If you factor in some error here and there, one could easily surmise that it is indeed a 55 degree thread.

I am thinking about pouring a silicone mold of the thread, then casting a resin version so I can hack/grind away as I need at the resin copy to get measurements I need.

I will post a rough sketch of the numbers I have on hand shortly.

Just wanted to post up and see if anyone else has figured out the thread size on these.

https://www.amazon.com/Grip-Thread-Pitch-Gauge-SAE/dp/B004ROIU2A

If you don't have a gage like that one, it may be worth getting. I use mine a lot more than I ever thought I would.

I can see no reason why they would use a modified Whitworth thread. In 23+ years of machining I have only ran into a 55 degree thread once. Customer was making spare parts for an old pump of some sort that was made in England.

I suspect, if the radius in the valley is prominent, it is likely an aerospace thread (UNJ), though it may be that the insert used to create it was thread specific with a wiper, and had a small radius ground into it. The radius on the peaks would lend it credence to the idea of an insert with a wiper, though it could be as simple as an M0 at the end of the cycle followed by a dwell and spindle speed to allow hand polishing with Scotch Brite.

In any case I would be curious as to what you discover.

Thanks for input. I want to make a correction to an earlier statement. It looks to be a truncuated whitworth thread. 55 degree does appear to be pretty close. However, it has flats instead of radius at the peak/valleys. I have thread gauges at home and forgot about them. I did some checking and 6-7 TPI does not work. However I do not have a 7TPI gauge... so I doubled up and used a 14 TPI tool. No go. Worked my way up, doubling, quadrupling the numbers... I think a 27 TPI gauge fits... That gives me approximately 6.75 TPI. Seems odd. I will keep brainstorming.