On Mon, 07 Nov 2011 21:35:21 +0000, Fred wrote:

How does the tool "know" the bolt has been pulled as far as it can?
After all, you can get these in different lengths, so surely it would
have to pull longer bolts further to fully set them?

It's feel, as you pull the trigger there is some "give" as the petals
start to deform, easy pulling for a bit, then it becomes very solid
when the pyramid has been fully formed. I guess if one was well into
brute force and ignorance one could mangle the fitting but it would
take serious effort.

I can see that if it was under done, the "petals" would not have
opened fully, so would distribute the weight over a smaller area.

And possibly continue to deform to the correct place under load
loosening the fitting.

What is the problem of over doing it? Is it that it starts to draw the
fixing into the plasterboard, enlarging the hole?

That isn't going to happen with a setting tool. A screwdriver doesn't
give the same level of feedback and there is the temptation to
tighten things up too much. Particulalry if things have not gone
"solid" , these things go firm but not solid under the influence of a
screwdriver.

To use the tool, do you pull the "trigger" once or do you have to pump
it a couple of times?

Depends on the fixing some are longer than others... The small ones
take less than a single squeeze.

--
Cheers
Dave.