In order to understand the evolution of metal components in the rod and reel we need to review the definition and properties of alloys, hardness, and abrasion resistance.
While we commonly use terms such as "stainless steel" and "nickel silver", the chemical and mechanical reality is more complicated. An alloy is a chemical mixture of elements which results in different properties than either element alone. "Stainless steel" is a family of Iron (Fe) alloys (mixtures) based predominately on iron (Fe) with variable Carbon (C) and other elements. Nickel silver is a family of alloys based predominately on Copper (Cu), with a variable combination of Nickel (Ni) and Zinc (Zn). There are many mixtures of "stainless steel", with different properties, and there are many mixtures of nickel silver, with different properties, and so on. In addition, there are different treatments that can be applied to a single alloy mixture AFTER smelting that FURTHER change the physical properties of that alloy, either throughout or surface only. That is true of both aluminum, stainless steel, and most other alloys.. So simply saying “stainless steel guide” or “nickel silver line guard” leaves one with a range of uncertainty regarding actual hardness.
This discussion is most centered on the property of abrasion resistance, which is not the most commonly measured or considered (or listed) property of alloys. "Hardness", measured in a number of ways, IS both commonly listed and IS generally linked with abrasion resistance, but the two are not 100% equal and there can be exceptions. For practical purposes I am going to talk about hardness. And for the easiest "apples to apples" comparison, I will use the Brinnel Hardness scale since it is most easily available on the internet across the alloys we will discuss.
Taken as a group, the range of Brinnel scale hardness of the alloy families INCLUDING treatments seems to be as listed below:
Aluminum (elemental) 20
Bar Stock, Aluminum, 6063 60
Cast Aluminum alloy (A413) 80
Nickel silver 55-170