kraftwerk 

I tend to use WTB Comfort Zone Clamp-On Grips on my flat-bar commuter bike.
High time to replace them, but the little nuts are rusted solid and now also stripped-out, so, cannot get an alan wrench on there .. is it time for the hack-saw ?
You bike-shop-mechanics must come across this B.s. all day long. Sorry.

FBinNY 

Since they're trash anyway, try the easiest way.

Assuming you can orient the blade to cut through the bolt without touching the handlebar, that's a quick and cheap solution.

Or, if you have a power drill and quality bit of the right size, drill through the b bolt head using the rounded head as a guide.

If your drill is a just fit for the head, you only need to penetrate a few mm to separate the head from the screw. The drawback may be that these czp screws are often made from hardened steel which can be tough to drill.

*Scuba 

I have had success so far every time when lock on grips bolts get rounded out or very corroded. Spray some 99% rubbing alcohol under the grip and just work the grip back and forth. Should slide off just like rubber grips that have gotten oxidised and are hard to get off.

This technique works, since the lock on collars and clamps are only on the end, majority of the grip typically have a hard plastic cover that does not actually have great contact to the handlebar.

soyabean

Are you saying the little M5 nut on the underside has seized onto the bolt, so now it just slips round and round as the plastic grips can no longer grab?

I remove these all the time.

I assume the 4mm hex on the top of the bolt is fine. Hold that steady.

I drill out the nut from the underside.

After the nut is gone, I just pop out the bolt and replace it with a new set.

kraftwerk 

thanks guys ~ will try some of these methods.
The rubber has worn thru to the plastic and the bolts are frozen, they've served their time.