Yikes. I'm looking at this and I'm like, that looks familiar. Then I'm looking at the table & lamp, in the pic, and I'm realizing it's my nightstand.
I guess I posted those pics? Anyway, the middle piece with the bolt/wrench head will be needed (or some variation of it) to connect the adapter to the cannon if your using a Karcher K adapter.
So your screwed.
j/k.
You get it at Lowes or Home Depot for like $2 in the plumbing isle. I don't recall the exact size, but it's pipe thread and readily available (3/8" NPT ???). Just bring the adapter with you - it's the same size as the cannon. You will need a small piece of male/male threaded pipe to connect the adapter to the cannon - as each is female. The wrench head just makes it easier to snug down.