Gap created after Screw modifier Just a quick question, is it normal for there to be a gap along the surface of a mesh once the screw modifier has been applied?
There can be gaps but they're not inevitable. 


The Angle should be 360° so the edges line up.
The Screw value should be exactly the same value as the object's dimension in the relevant axis.
The highest and the lowest vert should have the same distance from the screw axis.
After applying the modifier, using Remove Doubles with the relevant verts selected and a large enough threshold should kill any small gaps. Without that, a Subsurf Modifier might produce a gap.