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Anthron AB-20

Front View: Closed Rear View: Closed
Front View: Closed Rear View: Closed
Front View: Open for Rigging Rear View: Open for Rigging
Front View: Open for Rigging Rear View: Open for Rigging

Technical Details

I acquired my Anthron AB-20 in 2017 as part of Bob Thrun’s collection.

The Anthron AB-20 is 105 mm. tall, 79 mm. wide, 34 mm. thick, and weighs 148 g.

Cam faceThe shell is a tall irregular shaped stamping made from 4.2 mm. aluminum alloy sheet metal. The stamping has one reinforcing rib behind the cam. The ascender is right-handed, as are similar ascenders made by others. A 15 mm. rope channel is formed in the left side and a smaller cam channel lies to the right. A hole drilled through both sides of the cam channel accepts a 5 mm. roll rivet. The rivet is centered 49 mm. from the inside of the rope channel. The cam and cam spring are mounted on this rivet. A 15.8 mm. sling attachment hole is punched below the cam, and a novel slot extends from the hole. This design facilitates sewing the ascender to webbing, or allows the more traditional carabiner attachment. A second, 13 mm. hole is also provided at the bottom. A 14.9 by 20.9 mm. oval hole through both sides of the rope channel provide an attachment point just above the cam, and a 15.0 mm hole is punched through the rear of the shell beside it. There is no cam stop.

The cam is a plated skeletonized steel casting. The cam radius increases from 38 to 52 mm. over an angle of 39°, giving a 24° cam angle. The cam has number of small conical teeth, all of which have their axes approximately in line with the corresponding radius from the cam pivot. The tooth pattern is (3.2)^2(1.2)^2(B) pattern, where "B" indicates a bar. There are two notches on each side of the cam face, presumable for mud relief. Unlike some other ascenders, the inner cam face radius appears to be constant. A spring-loaded manual safety bar is mounted on the bottom of the cam with a small semi-tubular rivet. The normal action of the spring holds the safety against the cam. When the cam is opened, the shell interferes with the safety bar, thus preventing opening the cam. If the safety bar is moved away from the cam (opposing the spring), it will clear the shell and the cam will open. At full open the safety can be released and the spring will hold the safety against the back of the shell. This provides a means of locking the cam open. A pin on the safety assists in operating the safety mechanism.

The front of the ascender has a "AB-20," a triangle and double arrow logo, "ROPES" and "ø8-13 mm" stamped on the rope channel. The rear is stamped with "CE0123," "Anthron," and a triangle and double arrow logo. "0301-A" is stamped behind the cam.


The following ascenders are all variations of the same basic design, made by the same company under three different names:

Anthron AB-20 Lucky AB-20 VauDe AB-20
Anthron AB-20 Lucky AB-20 VauDe AB-20

The Rollgliss R250 uses the same shell and cam, but has different attachment holes.

These are well-made ascenders and perform much like the Petzl Basic. All sharp edges have been removed. The cam teeth are very well done. The attachment points are simply holes in the shell, and although rounded they should have been beveled more; even so, I would consider their small radius too sharp for directly attaching rope slings. They are acceptably rounded for webbing, and the unique slot makes it easy to sew webbing (up to 35 mm.) in place. but considering the proximity of the attachment points to the main rope, I would recommend using a small maillon for most rope attachments in order to reduce the risk of sling abrasion. The upper rope attachment hole is located very close to the main rope. A carabiner through the upper attachment hole will probably drag on the main line. Note that such a carabiner will prevent putting the ascender on or off rope, so one's climbing system must be designed accordingly.

The safety is awkward to use with one hand (like the Petzl Basic). The cam is very well made. The notches don't seem to provide much help in muddy conditions - but nobody else's similar ascender works well either. I'm not sure what purpose the bar serves - several people have sent me emails telling me that the bar keeps the cam from closing and touching the shell. I agree, it does, but so what? Putting the ascender on rope does the same thing. Initially I wondered if the bar would interfere with using the ascender. It does not appear that it will, at least on 9 mm and larger ropes.