for advice, in assuming it's a vertical "tower" type situation, 1/2 cheseboroughs mounting the fixtures to the
truss have at least over
C-Clamp or other types of clamp certain stability and not cutting into the
truss advantages.
After this on the "
base plate" as I expect you are making to weight down the
base, given your
fixture does not sit atop the tower, you might want to go off center on the mounting to compensate for the weight. If nothing else and even if that,
safety that tower off from above so it can't fall. There is a formula for what weight from above equals torque to be countered from below as a load and a at least 5:1 necessity for
safety.
For bolts, one on
countersink would assume that the bolts holding
truss to
base plate will be wanting to be flush to the bottom of the
base plate. In that way flat-head screws should be used. A black oxide or chrome/zinc plated alloy steel
socket head (hex) cap screw is a suitable replacement for the standard hex
bolt. Alloy steel screws are considered in common terms "aircraft grade" or grade 9 or 10 as opposed to the normal
bolt ratings of grade 8 used for
truss.
A
flat head alloy grade screw of at least 5/8" given it's the same size as your hex
bolt you would normally use to attach
truss together would be something to look into. Otherwise at times a alloy grade butten head screw is often also used as a screw type. Same strenght as say a
socket head cap screw, lower cap of screw height. All stronger than a grade 8 hex screw but will tend to become the bearing
point when sticking below the
base plate.
Recommended that you go flush bolts. This way nothing sticks out and you have a large surface area to distribute the load.