1997 Mazda B4000, 5-speed, 4WD, 4.0L V-6

I think I need to replace what I am calling the "idler wheel."

Standing at the front of the truck, looking down into the space between the
radiator and the front of the engine I see the serpentine belt weaving its
way around several pulley wheels.  One of these is the tensioner wheel and
several others are attached to the alternator, AC compressor, etc.  On the
top of the engine, slightly to the left, between the top of the engine and
the alternator is an idler wheel -- the belt runs over it but it's not
attached to anything except its mounting bracket.

This wheel is squeaking and squealing.  It appears to be attached by a
hex-head bolt going from the front of the wheel, through the wheel's hub,
into a bracket on the block.  If I squirt silicone lube into the hub, it
quiets the squeaking for a day or so, then the noise starts up again.

It appears that replacing this thing is as simple as taking off the bolt and
bolting on a new one -- right??  What do I need to order?  Should I get only
a new idler wheel, or, should I get the bolt also -- anything else I'll
need???

Thanks.