Where was the knife made? If it wasn't made in the USA, it may be a metric thread ( maybe a M3 x 0.5 ?, 3mm = 0.1181 in.). If I remember correctly, the 4-40 and M3 x 0.5 are very similar in diameter, but the pitches are different.
One thing I did before I got a pitch guage, is to use another...