i thought 40 X 20mm bearings didnt exist?

while stripping down my new Torker DX20 i got to the bearings and low an behold they are 40mm OD and 20mm ID…?

isnt this the size that all the KH wheel users were looking for but no one could ever find?

crap cam photo attached

20mm bearing.jpg

oh i forgot. the numbers on the rubber seal say 6203-2rs

You may need to check the accuarcy of your callipers.

The 6203-2rs bearings are one of the standard bearing sizes used on unicycles. Most entry level unicycles use them.

They have an inside diameter or 17mm and an outside diameter of 40mm and a width of 12mm.

For those who are truly keen, you can tell a fair bit of stuff from that bearing code.


The first digit is the type code
6 = “single row deep groove ball bearing”

The second digit is the series number
2 = “light” (as opposed to extra light, medium, heavy etc)

The third and fourth digit are the bore size code
Some common ones are:
00 = 10mm
01 = 12mm
02 = 15mm
03 = 17mm
04 = 20mm

the 2rs suffix indicates it is a double sealed bearing.

The outside diameter (OD) of a bearing depends on both the bore size (inside diameter) AND the series. A more robust bearing has a larger OD.

Imaging you are designing a stronger unicycle hub which is going to be slightly larger in diameter. To get a bearing with a bore of 20mm for a thicker axle we could use a light series bearing with bore 20mm:

6204-2rs would do the job but is has a 47mm OD and a width of 14mm. This is quite a larger OD and a smaller OD would look better in a frame, plus it would be nice if it had the same width as “standard” bearings used in unicycles.

To get a smaller outside diameter you have to buy one from the extra light series, ie
6104-2rs which has a 42mm OD and a width of 12mm

The next one down is an extra light bearing (series 9)
6904-2rs which has a 37mm OD and a width of 9mm.

The 6104-2rs is the “most compatible” with previous unicycle bearing dimensions, despite the larger OD.

well my calipers zero out right on 20mm and i have some 40x19 bearings from a past Profile hub that i know have a 19mm ID and they would’nt go on and a regular 17mm ID bearing that comes on most uni’s would never fit.

Jagur’s alive! And he’s talking about unicycles!

Oh yeah bearings I have no idea.

thanx Tim ,im touched. ive been doing alot of thinking latly.

now were are all the bearing gurus? i checked again and there is no way a 19mm ID bearing will fit so it must be a 20mm and the OD is 40mm

edit: just for you Peter, i have a 17mm ID bearing and tried it, it wont even slip on to the axle.

Back in August, there was a discussion about bearings for the Summit.

I was hoping to find a 43mm OD bearing so I could remove the shim that currently exists around the Summit 42mm OD bearing. Based on your post, you say that if I get a “more robust” bearing, I might be able to find a bearing that is actually 43mm OD. Is that right?

It was determined that the Summit uses a 6004-ZZ bearing.

My Profile hub’s bearings say ‘6203-12-2RS’ on them. They are definitely 40mm OD, and ID is way bigger than 17mm. I wonder what the ‘12’ part of the code means. Looks like there’s more than one type of 6203 bearing!


I think the 12 is for 12/16 inch ID rather than the 17mm standard ID.


Heh, heh you Americans are so wacky with your antiquated units! :smiley: Why call something 12/16" which clearly simiplifies to 3/4"?

I think its so you can have a system of recording it easier. If you are using a number in a series (IE:6203-12-2RS), if you use the same denominator for all it is much simpler. Using 3/4 would not work. You would have to include both the numerator and denominator.

Hey Jag, on unicycle.com the KH freestyle uni KH freestyle uni claims to use:

Bearing: 20- x 40-mm sealed


Ahhh, I see. That would make more sense.

Yes, tis true that the KH freestyle has 40 x 20mm bearings, as opposed to the KH20 and KH24 which have 42mm OD bearings.

interesting, if the KH,F does use them then that would validate my findings on my Torker DX… i remember Kris posting once about the Freestyle saying the only differance in the frame from the trials was that it took 40mm bearings on the OD and since the kh axle uses 20mm for the ID, then it must be so…?

40x20mm is the size that everyone wanted back when the kh’s came out and the people that wanted to put a yuni or Nimbus frame on a kh hub couldnt find, they had to settle for the 42mm OD.

its seems like 40x20mm does now exsist, although it still doesnt show up for sale on any of the bearing sites that ive been to…so what the hell? :thinking:

I think the KH FS is a different axle. It’s a non-splined version isn’t it? Maybe UDC is mistaken. It might be a smaller axle and may be like 17x40 or something. i don’t know. Anyone with calipers and a KH freestyle wanna measure?

Edit: Haha beaten John.

I’m pretty sure that’s an error. The KH freestyle unicycle uses a standard square tapered hub. Standard hubs fit a bearing with 17 mm ID. I’m pretty sure the KH freestyle takes a regular 6203 bearing (17 mm ID, 40 mm OD).

oh flub!

yeah you guys are right, i think the KH,F is a regular 4 squared tapered axle so it is most likely 40x17mm

but either way, my new torker DX has a bearing that has a bigger ID than a profile 19mm and a 40mm OD. the 40 OD is easy to campare since i have several 40x17’s laying around and they all have the exact same OD…40mm

one other interesting note about the Torker axle is the bearing is pressed on to its resting place. unlike the Profile axle, were it just slips on. the Torker bearing must be pressed on to a “taper” so to speak, making it a much tighter fit.

BTW, i have tried to press on a 19mm Profile bearing just to see if it would fit but it wont, the ID is definatly 20mm (the 19mm slip on only to stop dead at the taper)

in this attached pic the shiny part is the raised “tapered” part where the mystery bearing ultimatly sits.

taper chucks.jpg


So has anyone managed to find any 40 x 20mm bearings for sale? I’ve called all the bearing shops in Auckland and nobody sells them.

Otherwise I may need to resort to a 37 x 20mm bearing with a shim…


well i havent…wish i could…if the new kh uni’s have a raized section kinda like a taper (as seen in the pic i posted awile ago) on the torker dx axles you could modifiy the axle, but i doubt it does since its a copy of Profile’s style.

The closest match I’ve found is 6904 bearings - 37 x 20 x 9mm. Maybe these will work with a shim.

I have used those bearing with a shim on some
Norco 40mm (40x17x12) frames.

You must use different spacers with those 37x20x9 bearings. I made 25 sets of aluminum spacers so that the splined KH hubs could be installed in those frames.

The key is finding the shim material.
I used Nylon. I would like to have aluminum
brass or steel but haven’t had the demand to spend anymore time looking.

You need it to be 1.5mm / .060 thou thick for each cap.

If you know where to get shim stock in that size,
let everyone know.

The easiest is still to just put a Profile with 40mm bearings in those frames. A little more money at first but the best thing in the long run by far.

Take it easy,