The JX-1 is the Ruger factory ten round black .22LR magazine for the Ruger 77/22 and 96/22 rifles.
It varies from the 10/22 magazine having a flat base and angled front end for the bolt action receivers, but is otherwise the same extremely reliable flush fitting rotary magazine design.
Please note the JX-1 should not be used in a Ruger 10/22, their wedge shape makes them tricky to remove.
You can’t go wrong with having extra magazines, whether it’s for fast loading at the range or in the field. Or, as a backup in case of loss, damage or muddy puddle encounters.