Anyone that has been reading my posts etc, realises I have a thing for forks and shocks. I have had the dreaded anodising wear on my 16 At twin. I have said before, and will say again, I think all 16 and 17 models will suffer the same fate. Alas, there are options. I had mine Kashima coated, thus far has held out well. But by the chance it fails, short of bolting on gold "O" forks. There is a cheaper option. (Edit, Kashima coating on my forks eventually wore through. Disappointed, but suggests to much flex in 16 to 18 outers. I feel that even the Kashima coated 18 outers will wear the same way. Hopefully not, would like to be proven wrong on this one. Time will tell. As of Dec. 2018, I have ordered outers and lowers adv sport fork bits. Hopefully they hold up ok. Will review them in time.) 2018 at twin outer tubes. These have been updated with a Kashima coat, but the slider bush to outer tube clearance is still a bit loose. Part number for this part, 51410-MKK-D01 This is a good enough option, but there is better. They are still the same tube, only coated. Still will flex a bit. Adv sport forks. This I feel is the better option. These forks as a complete set will bolt straight on. Same everything externally except the additional 20 plus mm travel. Will make front end sit up if you bolt straight on. Would need to sort rear also. Good option if you want the extra travel. The outer tube is Kashima coated and has a larger OD just above area where seal and guide Bush live. Reg af twin in this area is approx 51mm, adv sport is 55mm. Outer tube is same length as reg af twin outer. Lower leg is same length as reg twin outer. Even though they have longer travel, all internals are interchangeable. But some need other bits to fit in same cases. Some parts I don't recommend exchanging. Read on. The extra travel. This cames from a longer damper tube assembly. The lower leg and upper tube don't contribute to extra travel dimensionally. But, the lower leg has had the glide bush moved 29mm higher to accommodate the extra travel. This gives good overlap of fork tubes to reduce flex. You could run the adv sport damper tube in reg af twin forks, but there isn't enough strength in the outer tube, combined with low placement of slider bush. Not enough overlap of fork tubes. A rider sag of say 70mm, would pretty much have the bush sit below triple clamp area. Which is lower than current set up. Current set up sits pretty much in lower clamp area. Not advisable at all. Reg af twin slider bush location is approx 35mm from top. Adv sport slider bush location is approx 15mm from top. Aside from this, parts are identical. Even running the adv sport lower in reg forks, gives an extra 29mm overlap where bush sits. This helps reduce flex. This is another option. Here is a pic to illustrate. I run about 65mm sag, so this pic relevant to my set up. Red dot, slider bush location if you used adv sport damper tube in reg af twin forks. Not recommended. Blue dot, current slider bush location, with my set up. Reg af twin forks. Green dot, this is the slider bush location using adv sport lowers with reg af twin damper rod with either stock upper tube or using adv sport lower/ upper tube combo. In pic below, red line is top of Bush on reg af twin lowers. Green line is approx were bush lives on adv sport lowers. Quick summary of parts that will fit but need to be together. Adv sport damper tube and fork cap assembly. Longer tube, equals longer rebound needle. Adv sport rebound needle won't fit reg af twin due to length. Don't recommend this option in reg af twin forks, as stated earlier. If you like the look of adv sport fork cap, buy it, rebound needle screws out and replace with reg af twin needle. Not really necessary. The adv sport fork springs are longer. If you ran them, it would be advisable to trim spacer. If bolting reg af twin damper assembly into Adv sport upper and lower, you use all you current internals. Straight swap. As for the rest, dimensionally, all other parts fit. Different part numbers on some bits, but they fit. Seals, bushes, spring spacer etc are all 100% interchangeable. Adv sport outers tubes are a straight swap into stock triple clamps. Zero mods. The lowers are also a straight swap. This is my recommendations. From don't do to best option with oem parts. Don't. I wouldn't recommend using adv sport damper rod assembly in reg af twin forks. Not enough strength to accommodate additional travel. As mentioned above. Better, Run adv sport upper with reg af twin lower leg, This option is more than adequate. Will certainly be a huge improvement over the regular Af Twin outers. Best oem parts option. Adv sport upper and lower legs, using reg af twin damper assembly. You get less flex with stronger upper tube, plus more overlap of the 2 tubes. Plus you get Kashima coated outers. Part numbers, Adv sport upper, 51410-MKK-D21 Adv sport lower, 51425-MKK-D21 right side. , 51525-MKK-D21 left side. With this option, if you have had your current forks re valved, just bolt together with your springs also, and away you go again. Less flex, better wearing coating. Simply, what Honda/Showa should have done in the first place. The one thing I am not sure of is the slider bush to outer tube clearance on adv sport tubes. Leaky seals on reg af twin forks is in part from to much slop in fork legs. The seal doesn't like it. I run a shim, (0.05mm, gives total of 0.10mm when wrapped around), behind slider bush on mine to reduce slop. Forks feel better with it, and no leaks since. (Edit, I have measured the ID of outer tube and the OD of the lower leg where bush seats on adv sport fork bits. The adv sport outer tube has same ID as reg twin tube, 47.06mm, but the OD on adv sport lower where bush sits, has slightly bigger OD, 43.96mm vs 43.86mm. In the order of 0.10mm. This is the same amount as what I shimmed my reg af twin bush to reduce slop. I didn't need to run shim behind bush on lower on new adv sport lower.) I think I have covered it all pretty much. If not I will add what's necessary. Hope this is of some value. Edit, Just to add a little extra, @Greg the pole has put together some great articles and vids, with heaps of pics of his fork rebuild etc. The big plus is he has given a list of alternate seals that can be used. Thanks Greg. https://thetenerist.wordpress.com Edit, edit I have received parts, upper and lower legs. Have measured bits up and are posted further on.