Since there have been a few threads lately about the old brown or black 2 piece Mallory caps and buying them at swap meets, I thought I’d share a little info to help make sure you get the correct rotor for the cap. Yes, there is a difference. Somewhere along the line Mallory made a change to the contacts on the inside of the cap. Initially they were simply flat on the bottom of the contact. Then they made them with a notch. This change required that the contact strip on the rotor be shortened. If you put an “old” long rotor under a “newer” cap, it will hit. I’ll show you the difference in rotors in the pictures. From what I can tell, all the brown caps are the older flat type contact. The 8 cylinder caps have the part number 24004 cast into the inside. Sometime after the switch to the black plastic cap, they changed the contact design. When they made this change, they also changed the part number in the cap to be 4004. They simply ground off the 2 on the old design’s number, which can easily be seen on most caps. Of the approximately dozen black caps that I have owned, I only have 1 black cap that is the older 24004 style. Now, when I say that the newer cap has a 4004 number, that is NOT the number that the cap is marketed/sold under. That is simply the part number of the LOWER section of the cap. The whole 2 piece unit is actually 4001. I do not know the part number for the “older” variety, maybe 24001? Now the rotors. I am aware of 3 different versions. The longer one used with the 24004 flat contact cap, and 2 other short variations that are interchangeable and used with the 4004 cap. The longer version that goes with the flat contact 24004 cap has the number 24215B cast into it. The contact strip has a fat tip, and under the contact strip is a piece of spring steel that allows the strip to flex up and down on the rivet. The rotors I have seen like this have all been brown. The other 2 shorter versions used on the 4004 cap both have the 4215 cast into them, again showing signs of where the 2 and B of the earlier style were removed. One version has a fat tip, and the other has a narrow tip. None have the spring steel and are solidly riveted in place. All the fat tip ones I’ve seen are brown. I’ve seen both brown and black narrow tips. The actual part number on a package for the short rotor is 4215C. I’d assume the “older” long part number would be 24215 and a letter? In the pictures of the rotors, the left is the longer 24215B version. The other 2 are the short varieties. I’ve also shown a picture of the many different types of packaging the rotors where in over the years to help you spot them at swap meets. I couldn’t get any good close up pictures to show the differences in the contacts, but in the brown cap photo, you can at least see where the number is located. Again, I’ve also shown a picture of 2 different boxes the caps came in. I hope this helps you get the correct cap and rotor for your Mallory. I’m not an expert in Mallory’s by any means, just a guy who’s got a fetish for them. Some guys like wheels, some gauges, some intakes. I like 2 piece Mallorys.