I acquired my MSR Auto Belayer from Bill Ivanoff in 2007, but it dates from the mid-1970s.
The MSR Auto Belayer is 92 mm. tall (78 mm. for the red block), 50 mm. wide, and 16 mm. thick. Mine weighs 93 g.
The main body is a block of anodized aluminum plate, shaped like a rectangle with two corners removed to make pentagon. The long side is rounded to form a semicircular edge. There are five 14 mm. holes drilled through the plate, each well-rounded. The holes are evenly spaced in two staggered rows, with adjacent holes on 19.2 mm. centers. A threaded hole in one end of the block accepts a 9.4 mm. square-head anodized aluminum screw that extends through to an end hole in the three-hole row.
One side of the Auto Belayer is stamped with the MSR logo, "SEATTLE 8 USA," and "PATENTS APPLIED FOR."
The MSR Auto Belayer was marketed as an Auto Belayer, not for making dynamic cows tails, but is so similar to the anchor brakes that I grouped it with them. It also closely resembles many of the. The unique feature is the adjustment screw.
To rig the Auto Belayer, pass a little more than 2 m. the climbing rope through the hole farthest from the screw, around the side and through the middle hole in the row (in the same direction), and then again around the side and through the hole with the screw. Leave 1.8 m. of rope and then tie the free end to your harness. Clip into either hole in the two-hole row. According to the instructions,
Anchor the climbing rope above you and then hang in the harness. Adjust the belayer to the point where the friction portion just stops slipping through. Then tighten the screw one more turn when using braided rope or one and one-half turns when using twisted rope [this refers to Goldline, which was going out of favor in the 1970s - gds]. The six feet of available rope will absorb the energy of a twenty-five foot fall. If a longer fall is anticipated, increase the length of the friction portion, or tighten the crew one-half turn more.
I'm not going to go out and take 25-foot screamers just to test these instructions. Since I started climbing in the 1960s, I've never felt that I needed an Auto Belayer (or an anchor brake), but I have found use for dynamic cows tails. The Auto Belayer has a nice adjustment feature, but that is something that can be adjusted improperly.