The seal plate screw for the Garrett GT/VNT 15-25 turbo to the untrained eye looks like a normal screw you can buy from your local bolt supplier;
These screws are fitted inboard of the seal plate O-ring;
If a standard screw is used, it is possible for oil to work its way up the thread and leak into the compressor cover. To prevent this, the screw has a sharp feature under the head which digs into the seal plate creating the necessary oil seal;
Melett accurate replacement screws are made on special tooling produced to ensure our parts contain this critical feature.