My protected 3400 Panasonics fit fine in it, the width and height are easy fits, it seems like it is made for it.
Mine is a number of years old, so I don’t know if the manufacturer changed the dimensions or not, but they are cheap enough to check out, they can also fit into a lot of knife holsters to carry on the belt.
Found some of those 2piece plastic rectangular storage containers for end mills
at the Swap Meet today—they looked plenty protective and
water resistant—but the seller would not sell them separately from the mill cutters.
Found a perfectly sized silver “pill container” for holding a spare 18350/16340 battery @ DollarTree stores
Not super sturdy—may be pot metal or plastic— but perfectly sized to hold a 18350
rattle free with no extra space.
Has o ring and key ring attachment, gonna add to my Bug Out Bag