These over - the - road heavy duty truck axle shims are a fast a nd accurate means to align front or rear axles of most popul ar tandem trailers and trucks. Specialty Products' new Zinc Alloy shims offer another level of performance versus our tr aditional aluminum shims. For a small cost increase versus a luminum, you now have the hardness of our premium manganese bronze shims and a much improved compression strength as com pared to aluminum shims.NOTE Order one Part Number supplies six shims in a box. California Residents WARNING