Kind of on the periphery of the charter so please do a direct reply if you have
info and think it is too far afield.

I am attempting to create a work holding device or jig to hold some stuff while
I work on it with hand tools.

I think the basic question is:  do any properties of what a magnet attaches to
affect the strength of the bond?

Short question that gives a feel for what I want to do:
Magnetic bases for dial indicators are switched so you can engage or disengage
the magnetism.  Is the hold strength of the magnet affected by the mass or
thickness of the iron that it will attach to?  In other words if I use a piece
that is 2 x 3 x 1/8 will it result in less grip than say using a piece that is 2
x 3 x3/8?

Longer question with more specifics:
When using a hand screw the reach is limited by the length of the jaw from the
threaded rods.  I am attempting to create something that would not have this
throat limitation.

I am using a Magswitch (https://www.amazon.com/Magswitch-8110005-MagJig
-150/dp/B001B8HMKG/ref=sr_1_2_sspa?keywords=magswitch&qid=1555873085&s=gateway&s
r=8-2-spons&psc=1">https://www.amazon.com/Magswitch-8110005-MagJig-150/dp/B001B8
HMKG/ref=sr_1_2_sspa?keywords=magswitch&qid=1555873085&s=gateway&sr=8-2-spons&ps
c=1) in one jaw and a piece of mild steel in the other jaw.  I am currently
using 1/8 thick steel.  If I try and hold two pieces of veneer between the 2
jaws it holds well, 2 pieces of 1/8 thick stock and it holds, but not well.
Does altering the thickness of the mild steel side effect anything?

Here is a picture of the prototype holding some 1/4 inch stock (it actually will
be 2 x 1/8+ pieces that I want to work, that I need to maintain the orientation
of and cannot use glue or carpet tape to hold together)

https://www.edoii.com/auction/magswitch/img_1981.jpg
https://www.edoii.com/auction/magswitch/img_1982.jpg
https://www.edoii.com/auction/magswitch/img_1983.jpg
https://www.edoii.com/auction/magswitch/img_1984.jpg

I bought a piece of 3/8 flat bar stock from HD and the hold appears to be
slightly  better than with the 1/8 bar stock I already used.  I don't want to
cut it up and make another prototype just to find out the hold is going to be
just nominally better.

Any engineering types out there that can point me in a direction?

Thanks,

Ed O'