I think it's the extended adapter not sure it applies to the 3-bolt. It's in the instructions.
If you're getting cleats they should come with whatever you need.
Everything you need for 3 bolt is included with the pedals, including a couple of different bolt lengths. Adaptor plate adds a couple of mm to stack tops.
Thanks.
Is that the 3-bolt to Speedplay adaptor (which I would need to use)?
Are those bolts included and if not are they just regular ones, or something proprietary?
I remember reading that the adapter enables a more mid-foot position, which I fancy giving a whirl...