Bill, glad to be able to help on this topic.
You can use any kind of glue, its role is limited to drilling and screwing in the longer threaded shank.
In fact, you fix it against falling out again.
Because the M3x10 mm screw screwed into the aluminum heatsink can sufficiently secure the FETs to transfer the amount of heat they produce to the heatsink. The M3x10 mm screw may be sufficient for fixing, because this size screw is not visible from the back.
Since I had such a metric screw, I added this, but you can also use a so-called metal plate screw if you can find one in this size.
Then you don't have to drill a thread into the cooling fin, because it can be screwed directly into the D=2.5mm hole.
You can use any transparent foil adhesive and use a vacuum cleaner to remove the shavings from drilling.
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Gyula HA3HZ
HA3HZ