Neumann K870/K87/K67 Capsule Types Through The Years: How To Identify and Date
Here is a rough overview of the K67/87/870 capsule generations, from earliest to current. To illustrate, I will add photos, just not right this minute.
1. The first generation was similar appearance as K47/49, but with two backplates mounted against each other with four M2 screws (if I recall correctly). Brass diaphragm rings, no threads in the backplates to mount the capsule which was held in place by two wire springs mounted on the head assembly, ca. mid to late 1960
2. Same as above, except for the mount: the capsule was held in the mounting ring via three pointed set screws, similar to M7 capsules, ca. late 1960
3. Same as above, but with eight M2 threads in the two backplate halves (2x4, offset from each other), ca. 1961 to 1964
4. Same as above, but with brown fiberboard diaphragm rings replacing the brass rings, ca. 1964 to 1966
5. First generation of plastic diaphragm rings (ivory color), whose mounting screws were recessed into the plastic, to be flush with the ring's surface, ca. 1966 to 1980
6. Same as above, but with white instead of ivory-colored diaphragm rings
7. Same as above, but diaphragm mounting ring screws no longer recessed, since late 1980s
Versions six and seven went through several generations combined; their subtle differences through time are only noticeable to an expert. Likewise, it's initially not easy to separate a K67 from a K87 by looking at it. Only upon closer inspection can you see the 40µ aluminum separator ring between the two backplate halves on K67/870.
Since the 1970s, all K67/87/870 are marked with a single digit indicating the last digit of the year of manufacture (i.e. "7" for 1987, 1997, 2007, etc.) This can be confusing for a layperson, because numbers repeat every 10 years. But the combination of build characteristics and date number allows pinpointing the year of manufacture fairly easily.