As you see here this has the "rocker" two bolt slipfitter with the bolts on top.

Why did GE stop making them this way? And why were the slipfitter bolts on top?

Powerlite had the rocker type slipfitter on almost all of their lights, I believe the reason these stopped being used was that they can eventually loosen and the light will end up sagging, of worse yet; fall.

I've noticed that the R47 also has a tendency to show lazy lineman syndrome although at a lesser extent than the 115s.

Oh Niall, what kind of slipfitter did the early Powerlites use?

You can see here , it is a kind of bolt set up.

My M-400's insides are very similar. The slipfitter is exactly the same and the PC socket in mine has that square plate too. The rocker fitter here has never slipped on the GE's. GE used riges between the rocker and the top housing. One the slipfitter is tightened, it cannot be adjusted. And the top bolts were just for easy installation. I wish they sill did that. I couldn't imagine mounting my M-400 on my yardblaster arm without the external bolts.

I bet you could of mounted it with the bolts inside.

Square plate? You mean the clear thing? I guess the M-400 Didn't come with a PC socket with it?

See that metal ring inside the clear plastic cover? It's circular on the outside and square on the inside. And yes, my M-400 did come with a PC receptacle. The metal ring is what holds the PC receptacle in place.

it could also be using Astrodome PC...which was made only for GE mostly on the older powerdoor streetlight like this one.....

He already said this had no PC socket. I don't get atrodome PCs. Why were they used? Was it so that they weren't falsly turned off by headlights?

The fixture also looks more streamlined with a Astrodome PC compared to a regular one.

I personally think cobraheads look better with a twistlock PC versus being flat anf boring.

That sort of depends on the fixture design imo.

Astrodome PCs uses plug in....not a PC socket......but since this fixture is from 1982...it may be too new to have one.......most of them were 60s and 70s as far as I remember....I may be wrong...

This didn't have a PC on the power door, so I know it wasn't one of those.

I think they just used a plastic cap over the PC recep hole. Check out the M-400R2/A2 replacement parts on their website. They offer a black cover and a clear cover.

I thought the M-400 R2/A2 had the PC socket hole just not there? Like the metal wasn't cut at all.

I thought they covered up the PC socket with a piece of metal like one of those KO fillers.

They use metal now like in Ian's R2, but the 70's lights had plastic caps from what Nimo said on mercuryvapor123's M-1000 pic.