I found a comprehensive chart for identifying hand-sewing needles:
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The pictures are said to be exact size when printed on A4 paper. I'm sure they'd be a bit off if I printed them on letter size, but there is also a chart giving the length and diameter in millimeters, and I saved it to my desktop.Another caveat: measurments for John James needles might not match other brands of needles -- but I buy John James whenever they are avaiable.