re Samuel's post above; the longer ferrule is indeed sealed and if it is not lubricated, or is lubricated with the wrong stuff, it will tend to go a bit draggy. It can be identified by
- longer length
- flats on end
- three grooves instead of two in the body
There is a small 'O' ring seal in the base of this type of ferrule. Needless to say the sealing efficiency/drag is also dependant on the exact size of the cable. Once the seal is worn, the sealing is lost, obviously. Also note that if these ferrules are seated in a badly shaped cable stop, the end of the ferrule can be deformed which then causes the O ring to go draggy on the inner cable.
Ref the small parts pdf, this is my take on the uses of the various ferrules listed, which others might find useful
1, 2. Unsealed steel ferrules for gear cable, various end diameters (to fit different cable stops)
3. Ridged plastic ferrule for gear cable in current road STI shifters; fits levers with a suitable groove (as per Feanor's kit). If these are surplus to requirements (eg because your shifters don't use them) you can remove the ridge you use these ferrules in other locations where a short tail might be useful.
4. Plastic gear cable ferrule with long tail; use where gear cable enters/exits a carbon frame with a bare cable run inside it, also where the a cable stop is angled badly to the bare cable run. Can also be used (in some cases) to provide a liner through the length of a barrel adjuster.
5. Plastic or Alu 'sealed' gear cable ferrules with various end diameters. Use metal ones where the drilling through the cable stop (for the inner cable) is oversize; this will prevent 'punch-through' of the housing which is otherwise likely with plastic ferrules.
6. Sealed gear cable ferrule with rubber boot. The tongue on the plastic part (which can also smooth the run through a kinked cable stop as per 4) usually has a barb on it so that the rubber boot won't slide off. This ferrule is the best one to use on (say) an MTB seatstay cable run into the rear mech; the crud only penetrates into the main part of the cable housing comparatively slowly. Occasionally it is prudent to use this kind of ferrule on a chainstay cable stop if the bike is routinely used in very mucky conditions. [NB some other manufacturers offer a similar arrangement whereby the boot is a concertina that is fixed to the cable inner above the ferrule, and is intended to compress/extend by the full throw of the shifter. IME this offers better sealing until the boot chafes through. A further variant has a long boot that moves with the cable inner, and the tail on the ferrule is long enough that the boot always covers the end of the tail, thus deterring crud ingress. This type is good to use on Moultons; with their dismally positioned cable runs they don't last in the weather otherwise.
7. Alu ferrule for brake cable outer, with plastic 'tail'. Use (where possible) in brake levers.
8. Alu brake cable ferrule sized to fit shimano MTB parts
Missing from the list is the miniature 'tail ferrule' that appears in 11s rear mechs. This also fits earlier mechs and helps to smooth the cable run in the high gears especially.
Confusingly BL-R400 etc appear not to require any kind of ferrule, but if you can find one that fits, by all means use it. I think you can fit some ferrules with a 5mm nose (larger ones will usually jam in the lever IME), but it is unclear if they actually do any good unless they have a liner through the nose.
For the gear cable runs I'd suggest a sealed ferrule (of some kind depending on usage condition) at the chainstay cable stop and unsealed ones elsewhere. Fit a 'tail' or a tailed ferrule in the rear mech if it will fit. If the housing run into the rear mech sees a tight bend (which is better avoided IMHO) or the mech uses a slotted cable stop fitting (i.e. with no barrel adjuster) then you may want to use an aluminium ferrule into the rear mech because the plastic ones can fail too soon otherwise.
cheers
