The common alloy used for bike frames were chrome-molybdinum which is referred to as ChroMo. I didn't know Manganese was used on some tubing until I ran into this blog. The alloy is called Mangy.
The link above shows how the Ritchey Logic came out of the Tange Prestige tubing.
The flow of Centurion serial numbers has died down, so it's an appropriate time to thank everybody who have so graciously submitted data on their bicycles and to present the findings of my study. 1980-1990 Japanese models: Japanese models during this period use a serial number format WXYZZZZ where; W = a letter, purpose uncertain, but probably indicates manufacturer or Centurion X = a number, indicating the calendar year of manufacture Y = a letter, indicating the fortnight of manufacture (A = wk 1 & 2, B = wk 3 & 4, etc) ZZZZ = four digit number, probably indicating frame number during fortnight Example: N4E0283 indicates the 283 frame manufactured during the period of weeks 9-10, for the year 1984. To date, I have rec'd 19 samples that fit this format. All but one use "N" as the manufacturer indicator. There is a minor variation of the above format, for which I have two samples, both from 1984. This format does not use a letter for the first character and uses a five digit frame number (ie XYZZZZZ format). The first number still appears to be the calendar year of manufacture. It is unclear if the following letter represents a month or fortnight of manufacture, however given a five digit frame number, it is probabaly a month indicator. Katakura Manufactured Frames (1980s) Serial number format Kfyxxxxx, where; K = Katakura f = letter indicating month of calendar year (i.e A = January, B = February, etc.) y = number indicating last digit of calendar yaer (i.e. 4 = 1984, 6 = 1986, etc) xxxxx = numbers, probably indicating sequential manfacturing number during month Example: KG511505 is 11,505th frame manufactured during July 1985. Late 1980s, early 1990s Taiwanese models: Sometime in the late 1980s, Centurion / Diamondback started sourcing Taiwanese manufacturers for some of their lower level models. The format varies somewhat and I have a limited number of samples, but in all cases the first number appears to represent the year of manufacture. The serial numbers vary from 6 to 9 characters in length and may, or may not, include a letter as the first character. 1970s models: This group consisted of few samples and several formats. Unfortunately, I do not have sufficient Centurion literature from this period to correlate the data to model years and any statements on the serial number foramt would be pure speculation. One cautionary note pertaining to the year indicators is that they appear to represent a calendar year and not a model year. Frames produced in the latter portion of the year may be production for the following model year. Unfortunately, there is no way of knowing the cut-off point and it probably floated somewhat from one year to the next. In such cases, you need to use graphics, component mixes or other tools to positively identify the year. Hopefully, this will be of some use to Centurion owners. I am still willing to accept data on Centurions / Diamondbacks and help in dating models. Hopefully, we can get some more data for 1970s and Taiwanese models. Again, thank-you to all the forum members who participated.