The sifter
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What it does
A sifter fitment meters a fine powder through a perforated disc so a user can shake out a small amount without tipping an open jar. For mica that is the whole usability of the product.
Why it matters commercially
Expensive powder spilled is expensive powder wasted, and a workspace clouded with mica is a complaint. A customer who has used a sifted jar does not go back to an unsifted one.
Thirteen is a short list
On a shelf of 549 closures. If a sifted jar is the product you intend to sell, the neck finish is decided by which of those 13 exists rather than by anything else.
Which is the ordering lesson
Choose the fitment, take its neck, then choose among the jars that carry that neck. Doing it the other way produces a jar you like with no sifter to fit it.
It blocks if the powder takes up moisture
A sifter disc is a set of small holes, and a slightly caked powder blocks them completely. So the liner and the seal matter twice: once for the product and once for the fitment.
A spoon is the alternative
Supplying a small scoop with a wide-mouth jar is cheaper, works, and reads as less finished. For a wholesale size it is often the better answer, and for a retail jar it usually is not.
Test it with the actual powder
Particle size and coating change how a powder flows through a disc. A sifter that works with one mica can block with another, which is a thing to discover before a hundred jars are filled.
An inner seal under the sifter is worth it
A foil or film seal beneath the fitment keeps the product dry in transit and gives tamper evidence, and the customer removes it once. It also stops the sifter clogging before the jar is ever opened.
Check the hole size against the material
A disc sized for ground spice is not sized for a coated mica. Too small and it blocks, too large and it pours, and the only way to know is to run the actual powder through it.