The Delrin bearings are crucial for two reasons.

#1) Prevent metal-on-metal sliding... which eliminates the need for oil as lubrication.

#2) To prevent jaw pivoting when only one side of the vise is being used.

Here is what was happening:

That pivot is abhorrent and detracts from the overall grip strength. It is known, that you are supposed to compensate for this effect by clamping something of equal size on the other side of the vise.

...or, we can design the vise to prevent pivoting with this handy dandy bearing mod:

There! .. That should keep it from turning. It certainly slides nicely!

Let's test it out on that bolt again:

Hooray!! ..:: And the crowd goes wild ::..