It was common practice in the industry to utilize lesser grade material in the stays and forks. This reduced manufacturing costs while still allowing the manufacturer to apply the higher grade decal to the frame.

This practice could be used on bicycles of virtually any level. In the 1980s it was not uncommon for entry level bicycles to have plain gauge CrMo in the main tubes but hi-tensile in the forks and stays.

I recall one case where only the seat tube was plain gauge CrMo and the rest of the bicycle was hi-tensile. The sole CrMo tube allowed the manufacturer to apply the CrMo sticker to that tube. I'm sure most buyers thought the whole frame, or at least the main triangle, was CrMo, but if you looked at the decal closely, it stated "seat tube" in very fine print.

Some models, typically racing bicycles, also often use heavier gauge materials in the down tube and chainstays to stiffen the bottom bracket for powerful riders. For instance, Columbus SP down tubes and chainstays are often substituted in otherwise SL frames.

Any number of mixes could occur to tailor ride characteristics or costs. In the late 1980s aluminum frames with steel stays and forks were fairly common. A number of current bicycles use metal main frames (steel, aluminum or titanium) combined with carbon fibre stays and forks.