@PRR1950 posted:I think I remember reading somewhere (so, don't quote me!!) that O scale in England was (and may still be) 1:43.5 scale. Thus, when Half-O was created (1/2 x 1/43.5), it came to 1:87. On the European continent, 1:87 translated to 3.5mm gauge and O translated to 7mm gauge. Also, if I remember correctly, in HO there is no difference between the scale size of pieces and track width (gauge), so the Proto87 guys are only worried about oversize flanges, oversized couplers, and other accoutrements that are intentionally oversized for ease of modeling and use.
Chuck
I definitely remember reading this somewhere, too. And since it makes perfect, logical sense, I would believe it to be true.
One small correction though, it's 3.5 mm and 7.0 mm to the FOOT, not gauge. But I knew what you meant. 
