Could be it's an 8.5. Threaded fasteners are always a bit smaller than the nominal diameter. It's probably a 1mm pitch or 25.4tpi. The radial slop would help to hide small differences in thread pitch such as 26 vs 25.4. Measure the distance between the tops of ten threads (peaks one thru eleven measure ten valleys) and divide by ten and you will know the metric pitch.
Last edited by garage sale GT; 08-20-11 at 08:05 PM.