I milled this eight from 12.7 mm. 6061-T6 aluminum plate in 2005, using a design published by Keith Likin in 1968 as a guide (Likin, K., "Figure 8 Ring. GCG Electric Caver, v3, #11, pp 87-88; reprinted in the 1968 Speleo Digest, pp. 3-43 & 3-44). Keith made his out of 7075-T6 using a band saw and file; I used a vertical mill to save effort.
My Liken is 152 mm. tall, 76 mm. wide, and 13 mm. thick. The rope hole is 80 mm. high and 52 mm. wide. The top center thickness is 13 mm. The shaft length and width are 28 mm. and 26 mm., respectively. The eye measures 33 mm. by 33 mm. My eight weighs 142 g.
The front-to-rear asymmetry is unintentional, and resulted from the concave milling cutter not being set to the exact center of the plate.
Keith wrote, "When testing this device, it was noted that it has a certain safety advantage over other rappelling devices. If by any chance the control rope gets out of your hand, the figure 8 ring locks so the descent is checked." He noted that this wasn't foolproof (I agree, so don't try it), and that "when the ring is locked, it is a first class job to get it unlocked. But I suppose being stranded hanging on a rope is better than being very dead."
My experience with being dead won't let me respond to the final comment (collect your own data if you're that curious), but I find it interesting that Keith actually tried to design an eight that would lock-off more easily than previous designs. Considering the plethora of Figure Eights With Ears designed to keep the eight from locking, I find the contrast interesting. Assuming a rappeller has the proper gear on, unlocking a girth hitched eight is no big deal, but there are times when having to do so is inconvenient.