Front	Rear

Left	Right	Open for Rigging

Technical Details

I acquired my Advanced Ropeclimbing Technology Lockjack Twin from Chris Gehrke in 2020.

My Advanced Ropeclimbing Technology Lockjack Twin is 49 mm. long, 106 mm. wide, 61 mm. high, and weighs 363 g.

The Lockjack consists of an aircraft aluminum body, a support line sewn from 11 mm. webbing, and a 12 mm. knotted kernmantle control line. The description is somewhat complicated since most of the pieces are irregular. The body consists of two main pieces" (1) a 28 mm. thick, 45 mm. diameter cylinder with two small projections, and (2) a 45 mm. diameter, 19 mm. thick cylinder bolted to the right side of the first. The first cylinder has the following features:

1. A 13 mm. slot milled across the top and down the front, 10 mm. from the end.
2. The projections point upward and slightly forward. These are drilled for a 6 mm. cap screw that holds the support line.
3. A second cap screw and washer keep the pivot cap screw from backing out.
4. A cap screw, bushing and nut hold a 20 mm. by 6 mm. round clevis at the top rear of the cylinder.
5. A knurled pin acts as a pivot for the cam to be described later. (The cam fits into the second block). The knurled pin is 58 mm. long with a 47 mm. active length. From the knurled knob, the active length consists of (1) a 1 mm. groove, (2) an 0.5 mm. shoulder, tapered toward the free end, (3)16 mm. of 7 mm. x 1 mm. thread, (4) a 2 mm. gap, (5) another 8 mm. length of thread, and (6) the remainder as a smooth 6.3 mm. cylinder.
6. A cap screw in the axis of the main cylinder supports a 1 mm. spring wire. One end fits in a small hole near the cap screw, the other extends beyond the cylinder perimeter, where it bends back and up into a 1.5 mm. wide slot cut in the lower rear. This spring acts in the 1 mm. groove in the knurled pin to keep it from coming out inadvertently.
7. The brass tube holding the control line fits into a hole in the base of the first cylinder.

The second cylinder is cut away on the side bolted to the first, forming a 15 mm. wide, 30 mm. deep rope groove on the rear of the device. The cam is a chordal segment of a circular disk, cut away on the flat side and the top corner with a concave surface to match the rope diameter. The second cylinder is attached to the first cylinder with two recessed hex-socket cap screws.

My Lockjack Twin has the ART tree logo with"ART" underneath stamped on each end, and "ADVANCED ROPECLIMBING TECHNOLOGY" above. A sticker on the front has "TOP" between two up-pointing arrows, "Lockjack" and "PAT PEND" within an ellipse, "TWIN," "MADE IN GERMANY," and "CE 0299." A sticker on the cam has two up-pointing arrows and the word "TOP." The two cap screws holding the cylinders together are marked is marked "IN•VI" and "A2•70."

Comments

The Lockjack Twin is similar to the Lockjack Sport, with the primary difference being the knotted control line on the Twin replacing the short line and wooden knob on the Sport. My Twin appears to predate my earliest Sport, since my Sports have pivoting arms, while an instruction manual found on the web shows the Sport with a sewn webbing support line.