Bridge string spacing adjustment help please

[Grooverjr]

I bought a body a while back and have just got to the point of being able to add the neck (hooray) so it's the first time I have noticed the string spacing setup -  and it varies currently between 20 and 15 mil between different strings. I want to get it back to the comfy 19mm everywhere but I can't work out how to adjust the black barrel bits. They seem like they should twist to move but I can't work out how.....

[floFC]

Have you tried loosening the black screw on top? It could be a locking screw.

[Grooverjr]

50 minutes ago, floFC said:

Have you tried loosening the black screw on top? It could be a locking screw.

That may be the thing. I thought it was a tilt adjust but there is no screw coming out of the bottom so it isn't that. I can't find a key to fit those screw holes at the moment, but when I can dig out the whole set I have I will give it a go.