This is a horn mouthpiece as made for Stefan Dohr, principal horn in the Berlin Philharmonic.
The Dohr model is similar to standard W2-2EM but this model has a larger bore. JK offers six cup depths for their horn mouthpieces: F: very shallow, E: medium shallow, D: medium, C: medium deep, B: very deep, A: more than that So this one is on the shallower end of the size range.
This M-series cup shape is slightly more brilliant sounding than the K-series. JK calls it "more round and flat cup" which makes little sense, but what they mean is the M cup is more bowl-shaped, with rounded sides and a shoulder at the bottom. The K cups are more of a long straight funnel as seen on many US mouthpieces.
This M-series rim has about the same curve on the inner edge as the K-series, but the M rim is flatter in the middle, making the contact area feel a bit wider to some.
Other specs are unknown but we ordered several "the normal way they do it", and one specifically for an Alex player, whatever difference that might make.
Pre-order above, ships in mid-June 2023 (and beyond). All mouthpieces are returnable for refund or exchange if they are in new and unmarked condition, fresh for the next player. We include a prepaid return label with mouthpiece orders.