This foot is not crmaillre is a worm that drives a pinion tooth lve the tube through the holes. Allows you to make small bridge lighting without big budjet (75 pice). If the load is not too heavy you can cheat a little with your foot up to 4m. It possde much a security pin, but not directly on the tube. It is positioned on the pinion. A plastic lever, spring loaded, may be removed and not to lose this prcieuse pin. Unfortunately, the pin is not very strong and wear quickly until no longer do its job. Tip: the holes well greased tube (tube or other fat). Otherwise, the teeth of the pinion puff tube rubbing. Feedback, a grind is harder mount and life trsrduite. Exprience with, you will do again this choice? Hard to say no. Although this is not a foot of quality for 300 (4 feet) can lift 200kg or dj do two small bridges, while the low-end pro feet - those with four feet - begins 300/unit to 100kg and 3m.