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Advanced Ropeclimbing Technology
Lockjack Sport
(#829, 2624)

Front Rear
Front Rear
Left Right Open for Rigging
Left Right Open for Rigging

Technical Details

I acquired my Lockjack Sport from Robert Jones in 2005. I acquired another in 2017 as part of Bob Thrun's collection.

The Lockjack sport consists of an aircraft aluminum body and a wooden knob attached by a 70 mm. length of 12 mm. kernmantle. The knob diameter is 42.5 mm. and the height 8 mm., with a 0.5 mm. diameter, 14 mm. deep recess in the base. The knob attaches to the kernmantle by the simple expedient of melting the end of the rope. The other end of the kernmantle is crimped into a 13.3 mm. diameter, 40 mm. long brass tube pressed into the main body of the Sport.

The remaining description is somewhat complicated since most of the pieces are irregular. The body consists of two main pieces" (1) a 28.3 mm. thick, 45.2 mm. diameter cylinder with two small projections, and (2) a 44.8 mm. diameter, 19 mm. thick cylinder bolted to the right side of the first. The first cylinder has the following features:

  1. A 13.2 mm. slot milled across the top and down the front, 10 mm. from the left side.
  2. The projections point upward and slightly forward. These are drilled for a 6 mm. cap screw that supports a pivoting arm with a 15.50 mm. eye. The arm is 60 mm. long and 8 mm. thick along most of its length, widening at the base to fit the slot. There is a small oil hole in the base of the arm that passes down to the pivot.
  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 47.8 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)15 mm. of 7 mm. x 1 mm. thread, (4) a 2 mm. gap, (5) another 7 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 kernmantle 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 15.2 mm. wide, 30.5 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.

My Lockjack Sport has a sticker on the right side with a tree ICON, "ART" underneath, and "ADVANCED ROPECLIMBING TECHNOLOGY" above. A sticker on the front has "TOP" between two up-pointing arrows, "Lockjack" and "PAT PEND" within an ellipse, "SPORT," "MADE IN GERMANY," and "CE0299." 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 "CS," "A2," and"70."


The Lockjack Sport is obviously related to Buckingham Lockjack. The eBay seller provided the following description:

LOCK JACK SPORT for use on 1/2in arborist … The Lock Jack is a precision mechanical device that allows ascending and descending in one unit. This very simple but secure rope brake works similar to a climber's friction hitch by pinching line when weight is applied. Unlike a friction hitch, Lock Jack allows incoming line to enter freely and nearly friction-free. Like its cousin the Petzl I'D, Lock Jack uses a clean aluminum surface to create friction instead of the standard fiber unfriendly, rope on rope method. Unlike the Petzl I'D, the Lock Jack allows incoming slack to virtually fall through the device during ascent or while limb walking. Both mechanical devices incorporate a handle that regulates grip to the line. We consider the Lock Jack more sophisticated than other options but suited more towards professional climbers, due to its high level of sensitivity. In the latter half of 2000 the German inventor Hubert Kowalewski redesigned the original Lock Jack and released two versions aptly named the TWIN, a small twin to the earlier model and the SPORT, a compact and fast reacting version that remains close to the harness. The basis of the redesign was to make Lock Jack longer lasting by incorporating a small clutch-like device that can be easily replaced upon wear (100 to 500 hours). Surface erosion to mechanical devices such as this is an issue greatly dependent on the amount of dirt within each climbers environment as well as the speed at which one descends. For this reason we highly recommend utilizing clean rope along with a friction saving device during use. The Lock Jack TWIN is much like its predecessor in that there is a long tether that keeps the device a few feet ahead of the worker. This version allows rapid hand-over-hand ascent by pulling rope out from behind the device as it magically advances ahead. The Lock Jack SPORT requires only 10 to 15 feet of rope weight below before really showing its stuff. Once the climber is a thrust or two above the ground, gravity drops line through the sport like water down a drain. Once aloft, the climber can move through thick canopy with the SPORT virtually unattended until there is need for more line. Most climbers will prefer the sport for its simplicity, low profile and supreme sensitivity. Both versions of Lock Jack are CE certified (the European standard) and meet all the strength requirements of ANSI. Two carabiners of choice are required for attachment to your harness along with arborist grade 1/2 inch (11.5mm) climbing line … with an eye spliced in one end.

I assume that the "original Lock Jack" referred to is the Buckingham Lockjack in my collection. As I wrote there, I'm not Tarzan, and leave serious evaluations to a real Tarzan who knows exactly how to use the Lockjack Sport in arboreal pursuits. Although I have the manual and understand the double rope techniques for ascending and descending, it is not obvious to me that the Lockjack Sport will reliably grip if I were to climb a plant and Earth's gravity suddenly concluded that I was a ground animal. As for myself, I'll stick to the safety of caves & cliffs.