The 9x19 50 Gauge is designed to be used with commercial 50-round ammunition trays approximately 6" x 2-1/2" in size. These are the middle range of commonly encountered sizes and many of them also work well as flip trays. (The smaller European size trays can be used with the 100-round gauge and a 100-round flip tray.)
The 50 gauges are made the same as our Shockbottle 100-round gauge, just less holes and wider spacing to match mid-size commercial trays. This is a request from customers that prefer to use those boxes for packaging. If you prefer 100-round plastic ammo boxes, the 100-round gauge will be a better fit.
If you have questions about use of the gauge, please see the 100-round gauge FAQs
(ignore the "which boxes work best" entry-- for the fifty, use the boxes seen above)
If you are not sure which way up the gauge is, look in the holes for the case mouth step. Some 50 gauges have the grip lines on the sides machined off-center to help show where the top is.