First let's clarify the two different styles.
The one with the round portion in the center is called "Clutch style G" and the more plain ones we're familiar with are called "Clutch style A"
Here's a nice page in a book with the description and pictures.
http://books.google.com/books?id=zh...nap-on%20clutch%20a%20or%20g&f=false

The bits webstershotrods listed above are style G, we're probably less likely to use that style.

Snap-on also offers the more common A style as 1/4" hex insert bits under these part numbers:
Bit, Clutch A, 3/32" Stock#: SDM242
Bit, Clutch A, 1/8" Stock#: SDM243
Bit, Clutch A, 5/32" Stock#: SDM244
Bit, Clutch A, 3/16" Stock#: SDM245
Bit, Clutch A, 1/4" Stock#: SDM246
Bit, Clutch A, 5/16" Stock#: SDM247

In adition to the insert bits Snap-On also offers some 1/4" and 3/8" square drive bits to use with your ratchet. (Some of them may simply be the insert bits in a holder, others are forged from one piece.)

Socket Driver, Clutch, Standard, 5/32" Stock#: TM31E
Socket Driver, Clutch, Standard, 3/16" Stock#: TM27E
Socket Driver, Clutch, Standard, 1/4" Stock#: TM30E
Socket Driver, Clutch, Standard, 5/16" Stock#: F30E
Socket Driver, Clutch, Standard, 3/8" Stock#: F29E

Note that they even have a 3/8" size, you're unlikely to find that size bit from someone else so keep Snap-On in mind if you run across a screw needing one.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-