On Fri, 05 Apr 2013 17:38:59 +0100, David Billington
wrote:

On 05/04/13 16:44, wrote:
Am Donnerstag, 4. April 2013 23:12:33 UTC+2 schrieb d32:
Take a look at B-24 drawn cup roller bearings. 1/4 OD X 1/4 inch long with a 1/8 dowl pin for a shaft. They are static load rated at around 200 lbs.
Ned,
Sorry, I only checked out Igus just now. They're headquartered in my city! I need to get my head out of my yellow bible sometimes! I figure that a 1/4" wide x 1/4" bore sleeve would need a minimum P value of 1900. I found a MDS-FILLED Nylon Bearing from McMaster with a P value of 2900. I see that Igus offers way way stronger options.

As to needle bearings, sounds cool, but I really want to use a 1/4" or 6mm brass shaft. It's not only the comfort issue with the luthier, but a 1/8" shaft might compress the wood too much. Many extensions are made of solid ebony, which should be no problem, but some are maple or other softer woods.
If you sign up on the Igus site they will likely provide free samples of
potential candidate bushes. I did this on their UK site and ordered the
bushes I wanted and paid for them and got a follow up call wanting to
know the application and volume and I explained it was likely a one off
but the chap said they would still have provided the bearings as free
samples, I presume this encourages repeat business and may lead to
larger orders. I expect you would do well to talk to or email an
application engineer there and explain the design requirements and see
what they recommend and get some appropriate samples. They sent me a
welcome pack containing more information and a variety of samples of the
range of products types they do.

Igus is a class act. I spent about $8000 with them in the last year,
mostly cable carriers and flexing duty cable. But they've been just as
helpful in the past when all I wanted was $15 worth of bearings.

--
Ned Simmons