When it comes to motorcycles, I generally prefer traditional spoke wheels, but when it comes to mags, nothing beats the look of the classic American Racing 12 spoke mag. I've liked them since the early 70's for their 3 dimensional aspect instead of the flat 2-D designs of other early cast or later billet mags. It's also because of their drag racing heritage and how they impart that drag/competition look on any machine running them.
With today's resurgence of vintage choppers and the increased re-interest in these wheels, I thought a few out there might be interested in an old article about the ones distributed by Performance Machine in the August 1978 Street Chopper.
Before we get to that, there's some confusion about their origins, manufacturers, sizes, and versions of the design.
Looking them up on the web I found some info that kind of adds to the confusion. For example:the 1973 ad below ( posted awhile ago), says these were made by U.S.Mag Corporation of Long Beach. Now I thought I remembered U.S. Mags as a competitor of American Racing around that period, but a source (below), explains how U.S. Mags was started by Parnelli Jones and his crew chief Art Hale Jr. in the mid 60's. The idea was to sell wheels that would fit the large performance tires Jones was selling at Firestone tire stores. It then states that Art Hale and U.S. Mags bought out a bunch of mag wheel companies including a small bay area company called American Racing and combined all of them under that name.
For more details go to: http://www.hotrodhotline.com/pr/2011/mht_us_mags_story/

So, who was U.S. Mag Corporation? I know American was once in Long Beach. It, also states these are aluminum like the later Cal Mags (in the Street Chopper article below), not magnesium like the earlier Americans.
Jerry Mills of Cal Mag with Perry Sands. Over the years there were slight differences like ribs on the back of spokes or shape of the hub area . Note that the pattern in the back has the flower shaped center hub that many early ones have.Although most folks associate these as being made by Performance Machine, both the caption and the article states that the wheels were produced and machined by Cal Mag and that PM distributed them along with brake kits.
An very unusual use of these mags.
Radir Wheels introduced their own version a few years ago. There's two problems, they are only sold in pairs and only size 18"
There are different sizes mentioned from time to time. Most people know of the 15" and 18" sizes, but there was a 17" shown on Rigid Hips blog. Then there's this quote by Jesse James on the Jalopy Journal 2-21-2009 : "I have all the Original hand carved wood patterns and pour molds for 15" 16" and 18" American/Performance Machine 12-Spokes....."