As of 2017, Subaru has been using two different oil drain plug sizes in their Forester 2.5L models.
If you search our size chart, you will get suggestions for both sizes.
The only way to know which size you have without manually checking it yourself would be to contact Subaru, give them your car info, and they should be able to tell you which drain plug you use.
If they identify your oil drain plug part # as 32195AA020, you'll be using our 108 series valves. If you're given any other part number for the drain bolt, you'll be using the 105 series valves.