Yours doesn't have a 1/2 written on it. There goes my tentative theory about the 1/2 indicating a rounded blade.
I have two identical #81's They are 4/8 full hollow round end, set in black scales, two pins. Carbon steel. Twinworks in english. Because I purchaced them together I always asuumed they were part of a multi-day set, or a weekender set.
Here is a Good Thread on Henckels SRs in the Straight Razor Place.. http://www.google.co.uk/url?sa=t&rc...2ZV3ed4x_M1UPp7eA&sig2=sA3CME_AzspUmFJzlgOp9A Billy..
I may have dated mine to 1933, or thereabouts, thanks to an old catalogue posted here: http://strazors.com/uploads/images/henckels_1933.pdf The quality isn't great but it says the scales are rubber, which mine apparently are and there is a number 78. On another page the gentleman marks the picture of the 78 1/2, which he restored and sold, this is next to the number 78. Interestingly the 1/2's do seem to be round tipped.
I thought it sounded like a really good theory. I wish I could read all of the information in that picture. Maybe they only made the 1/2 sizes round tipped.