screwing in thumbscrews??

[captainlip]

Can anyone suggest how to screw in the pins on the thumbscrews? I need to get another 5ish turns and it wont go in further as i cant find a tool suitable to screw it in, allen keys are all to big or far to small, small screwdrivers dont grab it enough to ger it in any further. Grabbing it with pliers ruins the thread on my last ones.

Im at a loss and i need to get another few turns in,

Thanks