Note this is like most dynabolts in that it is an expansion type locking system but unlike the standard dynabolt the flush head has a “nut” at the bottom of the bolt which will grab on the inside of the sleeve which will stop it from turning further. As you screw down the bolt it causes the fixed nut to rise pushing it up into the sleeve which forces the sleeve to expand locking the bolt into the concrete.
You will need to drill as close to the sleeve size as possible otherwise you may have to expand the sleeve further than maybe possible/practical. With our bolts you should be drilling no more than Ø11mm. To install simply drill your hole though the post base while it is in position and then “tap” the bolt into the hole through the post base and then tighten the bolt either with either an 8mm spanner or hex drive