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The Manual Belay MBA has an aluminum pulley sheave fixed between two aluminum side plates. The sheave is riveted to the side plates so that it cannot turn and so that the side plates cannot swivel. The latter point was overlooked by the manufacturer's technical writers: the instructions state "swivel cheek open and insert rope" which is not possible unless one drills the rivet out first - destroying the device.
The Single Rope Technique Manual Belay MBA puzzled me for some time. Their catalog lists it as a belay device, and states that "SRTE Static Pulleys (Friction Pulleys) were designed to be used as a BELAY DEVICE ONLY." The instructions state that "the rope is wrapped 280 degrees, once around the fixed sheave on the MBS and MBA models." Naturally, this wouldn't provide enough friction for a meaningful belay in hard-fall conditions, especially if the MBA was free to turn so that the rope only passed over 100°.
The true intent of the MBA is not described in its own instructions, but in a separate document on SRTE Pulleys. That document contains the following paragraph:
STATIC PULLEYS (Friction Pulleys) - These Pulleys were designed to be used as Belay Devices Only. Although not a true pulley, Static Pulleys (Belay Pulleys) increase the friction between the operator and the worker giving the operator more control... Usually used as the Second Safety Devices.
Although this is still ambiguous, I interpret this to say that the MBA is not intended to be the primary belay device, but is used where the rope is to be redirected so that additional friction is generated at that point. In effect, the MBA acts as a fat carabiner. The instructions state that "MANUAL BELAY [models]... are ideal for use where you wish to increase the surface area in the bight of the rope in case of a fall protecting and increasing the life of your rope" which might support this view, although in the instruction sheet the context of the statement is by no means clear.
Given what I can find out about the Manual Belay MBA from the poorly-written instructions, and given that the only way to rig the rope is to feed the free end through the opening between the side plates and sheave, I cannot recommend this device.
Single Rope Technique also makes an MBS model with stainless steel side plates.
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Like the Bassett Metal Studios Belay Spool, the Rescue Belay RBM is designed solely for rescue situations where lowering heavy loads is a possibility. It is similar to the Bassett Metal Studios Belay Spool prototype in many respects, and weighs essentially the same.
The spool is a 63.5 mm (2-1/2 in) stainless steel cylinder with two 6.7 mm stainless steel roll pins that act as rope guides. The side plates are 1.5 mm stainless steel bolted to the spool with 8 mm hex-head bolts (with washers). The side plates are stamped so that the edges are turned away from the rope. Each side plate has a slot and a second bolt and washer passing through a slot and into the spool. This arrangement limits the amount that the two plates can pivot to 45°, for a total of 90° with respect to each other. Although not strictly necessary, it does make the spool somewhat easier to rig. Unfortunately, the bolts are tight enough that the side plates do not pivot freely.
The Rescue Belay RBM uses a stainless steel drum while the Bassett Metal Studios Belay Spool's drum is aluminum. Under most conditions this allows the rope to run with somewhat less friction than the Bassett Metal Studios Belay Spool provides. This can be an advantage or a disadvantage, depending on the weight being belayed and the exact nature of the rigging. I see no compelling reason to recommend one over the other - buy the one that is sold in your hemisphere.
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©2007, Gary D. Storrick