Okay Sambo - I will chime in and add my own take on this
Thanks to Wez for much of the basic info...
RefretsIf you have a guitar whose frets are worn out or very uneven or simply not to your liking, then a refret is possibly in order.
There are wide number of fretwire gauges and types made worldwide
Some is American made, some is Dutch and much is far Eastern
Jim Dunlop wire has a good reputation (yes - the same company that lso makes picks and pedals and all that stuff)
Wire typesMost popular fretwire is made of "nickel silver" , although some players like the stainless (johnny Mac for one) and Warwick have long used a brass wire similar to what church bells are made of (apparently)
The stainless is very hardwearing, and strings seem to glide over it very easily, but it does sound bright and as far as installing it goes it is much harder work , and wears out your tools really quickly (which is one reason why we charge more for a refret with it - as we soon have to replace our costly tools after doing work with stainless.)
Wire sizesWire comes in a number of sizes - the main differences being in the height f the crown of the wire and also the width of the crown.
There are also a number of differences in the size of the tang bit that goes into the fret slot but that is more for the luthier to deal with rather than the player.
A taller wire will allow you to get more fingertip behind the string when bending which means that you can possibly have a lower action but still bend easily. It also reduces fingertip contact with the board which should reduce playing friction - although some player s may have to adjust technique a bit if they are used to feeling the wood under their fingertips.
Width of the wire can affect the feel and ease of using the wire. It also increases the fret's mass and can aid with sustain to a small extent.
None of this matters if the wire isnt put in well - a poorly done fret job can feel like cr@p no matter what fret size is used. A well done fret job can make even the biggest wire seem no so intrusive as the hand seems to glide over it.
I like using the biggest of wires like Dunlop 6100 or Dunlop 6000 on my own personal guitars as they allow me to play easily, and have an easy left hand technique - its what Tim likes on his guitars too.
Low/Vintage Wire - Dunlop 6230(old Fender & Martin) , Dunlop 6130 (70s Gibson)
Medium wire Dunlop 6150, Dunlop 6155 (as used by PRS)
Medium Jumbo Dunlop 6110, Dunlop 6120
Tall Jumbo wire Dunlop 6105 (thin) Dunlop 6100 & Dunlop6000
Fret DressingA fretdress is the process of getting all the frets on a even level with each other by levelling out any high and low spots. Also requires the frets to be re-crowned to a smooth dome shape to give more accurate intonation and a smooth feel. This process is often required to be able to get the best out of a set-up as it eliminates the high spots that may stop you getting the low action that you wish for.
A fret dress is often required where a guitars fingerboard has srunk a little as wood doesn't always shrink in an even way and this often results in high and low spots on a guitar neck.
We use the Erlewine neck jig as this gives a lot more control over the process and also allows us to simulate string tension on the neck whilst doing a fret dress,
