Bolts and Grips

Been out to Cheltenham today to pick some stuff up from Dunelm so only got pictures from this morning when I finally (Inshallah) sorted out my blowing exhaust.
When I changed the exhaust from the 'Straight Through', extremely noisy exhaust, to the standard Honda exhaust I didn't think it was much quieter.
Went for MOT last October and the service manager said he'd let me off with the exhaust, it was borderline. When I acted surprised he pointed out the 4 holes that had been drilled through the baffle at the back with the specific aim of making it noisier!
I've tried many resin adhesives with bolts to fill the holes, body filler, 'Steel Weld' expoxy and others to no effect. I kept losing the bolts so there may very well be a few cars driving around with bolts in their radiators as they must have come out of the exhaust like bullets!
Tried a Tap & Dye set that Luke loaned to me to see if I could get a thread to put the bolts in but the taps weren't long enough to reach the holes.
It struck me that after all of this, over the past 6 months, I needed something that can grip at the back and remembered I had some cavity bolts that you put into a hole and turn a screw that butterflies metal prongs on the cavity side.
Perfect, fiddly for the first one but once I got the knack of holding the non moving part with the Mole Grips it was easy, even used my electric drill which made the remaining three very quick to do.
My work here is done!!