The Silca Unocode 399 Plus Stacker:

It stacks keys and allows them to be processed by the automatic feeder. It can accommodate up to 95 keys with a thickness of 2,2 mm and up to 60 keys with a thickness of 3 mm.

The stacker is universal, and can accommodate most medium to large size inline keys. It has an adjustment for blade width, and the space between the head of the key and the shoulder. It holds up to 100 regular LW4 keys, or around 60 really thick keys.