Yes, it looks like the guts to one like this one. BTW, I would unscrew the existing extension and screw on a new extension and not mess with just the internal part. From your picture, it looks like a 4 1/8 inch extension.
When you unscrew the existing extension, check to see what manufacturer yours is and see if it has a number on it.
Also check with Freightliner. I'll bet that was a part they places on the wheel when they assembled the axle.
https://www.amazon.com/Milton-S-440-...alve+extension