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Bill..... ..generally OVERSIZE pistons are "stamped" with oversize in thousandths, but I'd guess yer "03" would be 0.030in or 30 thousandths. Here comes the "confusion factor", the N's dry sleeve scheme has constant bore or piston diameter of 3.187in or commonly called 3-3/16". Thousandths are never indicated. The steel sleeve is 0.040" thick, and the more desirable castiron sleeve is 0.090" thick. (why is castiron desirable? 'cuz piston rings seal better) The only time you really need to worry about the difference between steel or castiron sleeve is iff'n you haffta remove them 'cuz of excess wear. The ONLY way to tell iff'n you have excessive wear is by inside micrometer. (top, middle, bottom, at zero and 90 deg, thats 12-mike readings per cylinder) The the block holes will be 3.267" for steel sleeve and 3.367" for castiron. (a difference of 0.100") Sleeves are a "inference fit" meaning they are 1-3 thou bigger OD than block hole ID and must be "pressed in" during installation. (special tools are required, altho I advocate a dry-ice scheme) Ring end gaps as measured inside the sleeve before piston installation is: 0.010-0.017". Most ring boxes will also have the endgap spec'd too as well as iff'n oversized. While Ford changed to castiron sleeves at s/n: 8N433578 (1952 sidemount) and had a funny additional s/n stamp, this is NOT ALWAYS the case with earilyer N-Engines which many times have the engine block bore-out to accept the more desirable castiron sleeves. Did you know the answers to all yer questions are found in the I&T FO-4 manual? $25 (cheap) ..... ..HTH, Dell, the non-expert
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