I received a violin not too long ago that has metal screws in the pegs. I am unable to tune with the pegs due to this and I am unable to change the strings. When i try the pegs slip and won't hold tune. The violin is about 45 years old. My teacher is unable to tune it because he doesn't know how to use these types of pegs. I will attach a link to a website that has pictures of these types of pegs. http://www.maestronet.com/forum/index.php?/topic/329656-what-kind-of-pegs-are-these/
The screws sound like some hotfix rather than an intentional solution (or you are misdiagnosing the problem), so it would seem important that you follow up on the request for pictures.
The regular way to deal with slipping pegs is cautious application of a special sort of chalk. If they are too sticky, a special sort of soap is used for the reverse effect. Both items are available in well-stocked music stores.
However, first it would be a good idea to figure out what role said screws play in relation to your problem.
I've never seen pegs like that before and honestly I would recommend going to a violin maker's place and having them make new pegs for you. I had some really awful wooden pegs once and when I went in it only took a few minutes for him to size new pegs for my instrument.
Also a note on the other answer (because I can't comment) another quick way to deal with slipping (wooden) pegs is to use a pencil and draw on the part of the peg that is slipping. And then I have "peg drops" for sticking pegs that I got from some music place.
The pegs in the provided picture are probably Caspari mechanical pegs.
There are both friction and geared versions of mechanical violin pegs, created to replace the standard wooden violin peg. The advantage reportedly being finer tuning, less force required to tune and no slipping.
They came installed on new Roth violins for a while, I think in the 1950's or so.
For the friction style there is a ring of fibrous material that gets compressed by the screw to create the friction to hold the string, similar to how friction banjo pegs work. In some cases the friction ring is glued into the peg hole, and if it comes un-glued it won't work until repaired.
There is a brand that uses a threaded and glued install. I'm not sure what brand it is, but I did a removal and replacement on an instrument with some and it was a tough job. In this case the peg holes had been reamed out to take the large bushings and I had to install peg bushings to put wooden pegs back in.
There are currently geared tuners on the market today from a few manufacturers, and some custom built ones that can match existing pegs. Some of them require gluing in, others don't. Most of the manufacturers provide different bushing sizes so that no modification to the peg holes is required except where the peg holes have been reamed out past normal size already.