Jose wrote:

I'm guessing there were used in double shear


Whazzat?

Jose

It is when a bolt has two shear planes, which means the bolt passes
through three pieces of metal, with one being on either side of a middle
member. Hard to draw in ASCII, but I'll try:

X's represent the metal being fastened, O's represent the bolt

Single shear:
O
XXXXXXOXX
XXOXXXXXXX
O

Double shear:
O
XXXXXXOXX
XXOXXXXXXX
XXXXXXOXX
O


You can probably Google "double shear" and find much better diagrams and
explanations.

Matt