While some choose pickup rings to mount their pickups, this is not strictly necessary – you can also mount them directly to the wood in the pickup pockets.
Many guitars employ this mounting method and a lot of builders like to mount the telecaster neck pickup in this fashion; here is the low down on how it is often done. This comes courtesy of the TDPRI – the definitive Telecaster forum
“The screws need to be ‘wood screws’ with a sharp pointy point not machine screws (the image above looks like machine screws, done for just the diagram but don’t take it literally).
Use either foam or springs but you don’t really need both; unless you prefer to wear a belt with your suspenders.”
The important thing here is to make sure the mount points are secure at either side – you don’t want your pickup flopping around – and that if you use foam or suchlike underneath then make sure that it’s not forcing the pickup up in the middle – this will lead to broken coils and other horrible things.