This is mostly a curiosity question but I still have a front wheel that has these spokes.

Last month I had the displeasure of having several spokes break on a century ride.

The full story is here:

http://backroom.hardsdisk.net/rivervalley.html

The vintage Nashbar (Maruishi) touring bike was new to me and had one broken spoke when I got it. I also found an odd replacement spoke on the drive side, after the ride, when I rebuilt the wheel with all new spokes.

I weigh about 195. This 27", 40 spoke wheel, should have easily carried my weight and a few accessories.

All 5 spokes that broke on the ride, broke right at the place where the head (button) meets the spoke, before the bend (leaving an invasion force of 5 tiny flying saucers along the road somewhere). Spokes broke on both sides of the wheel, 2 on the drive side.

The original stainless spokes had an abrupt, sharp change where the spoke meets the head (left two, in picture). The new replacement Wheelsmith spokes have a more gradual curving transition at the head (right one, in picture). It seems to me that this is a better way to manufacture the spoke, with less of a stress riser.

I've had a couple of spokes break on other old bikes in the past but I recall them breaking at the bend, which I thought was the usual place for them to fatigue. Is it unusual for a spoke to break at the head?

Did these spokes break due to a defect that was just manifesting itself before I got the bike or was it just likely due to improper tensioning, made worse as more spokes started to break?

I only checked the tension by feel when I initially tuned the bike up and replaced the broken spoke it had when I got it. It seemed fine but the tension may have been tweaked by whoever installed the 1st replacement spoke before I got the bike.

I'd just like to get an educated guess as to why these spokes failed and if I need to worry about the front wheel, which has been fine so far but obviously hasn't had/doesn't get the stresses the rear wheel has.