Rear locking hubs?

I dont know if I'm calling them the right til g but I bought another 95 4runner as a part vehicle and got ot home notice the rear look like it has locking hubs. I'm attaching a pic can some let me k ow what exactly are I never anything like it before on a 2nd gen.

 

That’s just what they like without the caps.

 

Those are not locking hubs, that's just what the casting looks like, they don't turn to lock or unlock

 

Ok then he did something to my green 95 rear hub it doesnt have cabs and hubs are enclosed and round do any of y'all know whats up with that?

 

It has really good gas mileage whatever he did for a 3.0 I get 21 on the highway and about 15 to 16 in the city

 

It's a 4x4

 

Not sure if this applies...but...

Is the speedometer measuring speed correctly?

On the old muscle cars, people would swap rear diff gears to either get faster ETs or the other way to get better MPG.

But the speedo would be off especially at higher speeds...if the speedo is off, then there's a clue. Not sure if that is something people do on these cars.