Your measurements are essentially identical to what I measure on the older 900 series Hakko tips, within +-0.05 mm. The T18 series is the modern descendent of the 900 series, and they are backwards compatible (on hakko irons, at least). They are slightly larger in OD (about 6.80 mm) and just a smidge shorter in the depth of the hole (about 23.0 mm), but they index at the same spot on the shoulder. They probably fit your iron, but you might want to check that the OD is going to fit.