Perfect, matches the original perfectly, has the correct little details to mate with the base of the 500D/M and probably most others, Go to the people who know and care about phones, no some overseas manufactured who only cares about being just good enough to work for the lowest production cost. I am sure they buy them from some manufacturer out there, but they took the time to find the right manufacturer.
Here is an original set of Western Electric 500 series telephone jacks for modular handsets and cords. These break easily so it's best to keep some on hand. The line cord jack is a 623D and the handset jack is a 616D.
I purchased a 500DM a short time ago. The wall side (623D) modular receptacle appeared to be original to the phone; however, a part of the receptacle was broken allowing the receptacle to move in the opening. I found the "Old Phone Shop" thanks to some ad hoc 'Google Fu'... I ordered the pair of receptacles and a second 623D as a 'spare'. All three came in the gray plastic color shown in the picture. The originals were brown... so, that leaves me with my only suggestion - source both and let the customer choose the color. Regardless, I replaced both (so they match) and both fit perfectly. Very happy to have a working rotary dial phone! I am using vultr as a cloud hosted PBX provider with ClearlyIP SIP trunk. A Grandstream HT801 (ATA) is configured for rotary dial and sends and receives calls... GREAT project. So much fun... hope more people bring these things back to life.