oil pressure switch/sender

Hi,

My oil pressure sender was leaking when I bought the car, and I picked up another one locally. The unit they sold me is a "Standard Motor Products Inc" PS-153. I just went to the Standard web site, and this is the correct part #.

However, when I pull the old one out of the block, there is a little fitting on it between the sender and the block - it seems to be an adapter of sorts. The unit that came off the car is a little smaller than the PS-153, and the PS-153 has a much smaller hole for the pressure to be read from. However, it seems to fit into the little adapter-gizmo just fine, and does have the correct bullet-type connector at the back.

Do I have the right part? Was the one on my car the wrong part? Why the different aperture sizes?

Thanks,

Ayan

'74 260Z RLS30-0061XX