The hole length needs to be long enough to accommodate the full length of the anchor for maximum performance. The anchor must be flush with the surface. Therefore, if the anchor measures 1/2 inch it must be at least 1/2 inch. It is a good idea to have a small amount of extra space also, to accommodate the screw just in case the size should be a little longer than the fixture and anchor length combined.
The screw must penetrate the main body of the anchor as this fully activates the grip points. If the screw does not penetrate into the anchor, it simply will not do the job and the anchor will eventually start to move, so it is really important that the screw length is long enough to accommodate the fixture and the anchor combined length combined. It is recommended the screw being slightly longer than the anchor. The total length also needs to take into consideration the length of any fixture – for example bracket, that is being fixed.
I used mine with drywall screws. No issues
Why anchor into wood? Why not just a pilot hole and proper length wood screw instead?