I was tinkering with some random parts, and idly stuck a Technic pin into the bottom of a 1x1 brick. It fit well, but that's no surprise; Technic holes are of stud diameter, so of course Technic pins are, too, and they can go just abut anywhere a stud can go. The surprise was that it didn't go in all the way at first, and the bigger surprise was that when I pushed harder, it *did* go in all the way, and then clicked!
Closer inspection reveals that the inside of the 1x1 brick has some faint ridges molded into it, at just the right depth to catch the latching rims on a Technic pin. And it turns out that a bunch of the other 1x bricks have these ridges, too.
This leads to several questions: How long have those ridges been there? Do any official Lego models make use of the technique? How can they be molded and still maintain positive draft? And do the Ldraw folks have to worry about distinguishing between hypothetical 3005a Brick 1 x 1 with Pin-catching Ridges and 3005b Brick 1 x 1 without Pin-catching Ridges? (In particular, I notice that transparent 1x1 bricks don't have these ridges, probably for visual reasons, i.e. similarly to the way the transparent 1x2 and 1x4 bricks don't have internal studs.)
Steve Summit snipped-for-privacy@eskimo.com