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The keystone (shown in red) of an arch Dropped keystone at Colditz Castle. A keystone (or capstone) is the wedge-shaped stone at the apex of a masonry arch or typically round-shaped one at the apex of a vault. In both cases it is the final piece placed during construction and locks all the stones into position, allowing the arch or vault to ...
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A keystone module is a standardized snap-in package for mounting a variety of low-voltage electrical jacks or optical connectors into a keystone wall plate, face plate, surface-mount box, or a patch panel. Keystone modules have a rectangular face of 14.5 mm wide by 16.0 mm high and are held in place with flexible tabs.
The appropriate thickness of a layer of track ballast depends on the size and spacing of the ties, the amount of traffic on the line, and various other factors. [1] Track ballast should never be laid down less than 150 mm (6 inches) thick, [5] and high-speed railway lines may require ballast up to 0.5 metres (20 inches) thick. [6]
[1] [3] To prevent this, fluorescent tubes are connected to the power line through a ballast. The ballast adds positive impedance (AC resistance) to the circuit to counteract the negative resistance of the tube, limiting the current. [1] Several American magnetic ballasts for fluorescent lamps. The top is a rapid start series autoregulator ...
Slab track with flexible noise-reducing rail fixings, built by German company Max Bögl, on the Nürnberg–Ingolstadt high-speed line. A ballastless track or slab track is a type of railway track infrastructure in which the traditional elastic combination of sleepers and ballast is replaced by a rigid construction of concrete or asphalt.
Cross section of a vessel with a single ballast tank at the bottom. A ballast tank is a compartment within a boat, ship or other floating structure that holds water, which is used as ballast to provide hydrostatic stability for a vessel, to reduce or control buoyancy, as in a submarine, to correct trim or list, to provide a more even load distribution along the hull to reduce structural ...
Ballast is dense material used as a weight to provide stability to a vehicle or structure. Ballast, other than cargo , may be placed in a vehicle, often a ship or the gondola of a balloon or airship , to provide stability .