The twist mechanism
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The one component in this craft with moving parts, and the one most likely to generate a complaint about a product that is otherwise perfect.
A machine, not a container
A twist tube is a barrel, a threaded screw, an elevator disc that rides on it and a base that turns. The balm is cast around the disc.
Which means the product and the mechanism are one object after filling. A fault in the mechanism is not recoverable and the whole unit is scrap.
Where they fail
The disc jams, usually because balm got past it into the threads during filling.
The base spins freely without lifting, which is a molding tolerance problem and shows up as a whole bad lot rather than an occasional unit.
The disc lifts out with the stick when the customer winds it too far, and cannot be got back.
It will not wind down, so the cap crushes the top.
What to check on a sample
Before buying quantity, take a handful and wind each one fully up and fully down three times, empty.
Then fill three, let them set, and do it again. A mechanism that is smooth empty and stiff full is telling you the barrel distorts or the disc is a poor fit.
Check the disc is seated at the bottom as supplied, since a batch shipped with discs part-way up gives you short fills nobody notices until the weights are checked.
Buying them
Caps and tubes as a matched set from one supplier and one range. Mixed sourcing is where the seats-badly complaints come from.
And buy the same tube consistently. Changing supplier changes the internal volume, which changes the fill weight, which changes the declared net weight on a label you have already printed.
