Yes, they are much smaller than M20.
The bearings which came with my 47 project are:
bearing: 1/2" hole, height 13/16"
outerring: 1 5/8" outerdia, height 9/16"
and have number : 2K-CO162X, one is Skefko and one is SKF.
I will send you a photo of the bearing, Peter, photobucket is slow atm, good luck with your project, nice little bike with big engine...
Cheers, Michiel
You could order them from The Vintage Bearing Company but then you really need to have an AED present 
The quoted GBP 350 each for BSA M20 British Timken front wheel bearings...
email (option): leonhop3_at_planet_dot_nl
Then the quote I got at >200 quid was cheap!
Seriously though, we should just be happy that we can even get the damn things to let us keep the bikes on the road. It's still a lot cheaper than the average golf club membership!
Cheers
Pete
Hi Darren
Thanks for your help and advice. I’ll be back in touch as soon as I know what is what.
On the subject of Simply Bearings – I did recently order some bearings for the front wheel. These were described as “Brand / Quality: EU Budget - Economy Quality”. After delivery I asked them what the EU meant (I had naively assumed it was “European Union” and that they were made somewhere in the EU) and whether they were suitable for use as motorcycle wheel bearings. The answer was; not necessarily EU made and not recommended for automotive use. The bearings I got are Chinese made and, as even the stamping of the numbers on the cages is not consistent, I have my doubts as to their quality. 
My fault, I should have checked first, but I must admit to having the feeling that describing the quality as “EU” is a little disingenuous, although this may well be an industry term that I am not conversant with.
I would say that I have always been happy in the past with SB’s service and products! Quick delivery and prompt responses to queries. I should have asked before ordering and remembered,you get what you pay for!
Cheers
Pete
email (option): petercomley@web.de
Darren should be able to help...He kindly resolved the problem for me on my rigid B31 wheel...Ian
email (option): ian@wright52.plus.com
Hi Pete,
I have known bearings made in China to arrive in the UK with 'Germany' printed on the bearing and box.
Not 'Made In Germany' just the Country, this apparently does not breach import laws as it does not claim to be 'Made In..... just imported from, rubbish isn't it.
If you let me know your bearing reference or sizes that you have obtained, I will see what I can do to help, you have my email
I am finding this happening quite a lot due to the ease of being duped over the internet, but if I can ever help or advise on bearing selection, anyone is welcome to ask. I have over 30 years experience running my own bearings and power transmission Company, which although mainly industrial, much is the same especially in these older machines.
Darren
email (option): dwrudd at lineone.net
I have known bearings made in China to arrive in the UK with 'Germany' printed on the bearing and box.
Not 'Made In Germany' just the Country, this apparently does not breach import laws as it does not claim to be 'Made In..... just imported from, rubbish isn't it.
If you let me know your bearing reference or sizes that you have obtained, I will see what I can do to help, you have my email
I am finding this happening quite a lot due to the ease of being duped over the internet, but if I can ever help or advise on bearing selection, anyone is welcome to ask. I have over 30 years experience running my own bearings and power transmission Company, which although mainly industrial, much is the same especially in these older machines.
Darren
The most forged item in the world is bearings.
Bearings should only ever be bought from a specialist bearing supplier.
Even then their wholesaler could have picked up a shonky batch.
Crap bearing makers will put any name on the bearing that the purchaser requests.
First suspicion is the lack of grade.
I can buy 6302 off the web 10 for $ 6.oo listed as "fitting"a pile of uses.
Note it does not say suitable for any of them.
I can buy 6302 from my wholesaler for $ 12 each which I know are good.
there are a lot of what looks like a bona fide bearing shop on line that are nothing more than a transport warehouse tied to a web app.
email (option): bsansw1@tpg.com.au
Darren did a great job of sorting out my problem with the rear wheel bearings, thanks again! 
I'm not familiar with the girder front end bearings but I'm sure Darren or Ian will be able to give advice.
Cheers
Pete
email (option): petercomley@web.de