question: How does the tightening mechanism work on a hard hat.
comment: I expect there are several different models of hard hat out there, so my explanation might not be of use to you, but with the ones I'm used to: The head doesn't rest directly against the hard outer shell of the helmet but rather a mesh or piece of cloth connected to a ring around the outer edge of the helmet which is in turn connected to the shell. This ring isn't actually a closed loop but rather a strip of metal (or plastic) that is bent into one with the ends overlapping slightly. It is held in place by a knob that, upon turning, moves the overlapping ends further in one direction or the other, effectively changing the size of the circle. Think about it like adjusting a belt or wristwatch, only with a cogwheel instead of a pin and a hole. Then there are also mechanisms to adjust the chin strap in various places, though they all operate on the same principle as most places where you adjust the length of a strap: The strap gets broken up into two parts, one of the parts gets directly connected to a piece of plastic and the other gets looped through said piece of plastic in a way that presses against itself to prevent accidentally moving. You can then adjust the length by pulling/ pushing the looped part by hand.
passages: Strip or paper cap guns use the aforementioned cap strip in lieu of the cap ring. As in the ring style of gun, each pull of the trigger advances the cap strip forward, pulls back the hammer to the point where it releases, striking the cap.
   The strap is black, white or gray cotton webbing with interwoven rubber tensioners. Hardware consists of nickel-plated or salt-blued steel wire bails at either end with a stamped nickel-plated or salt-blued steel adjuster. The wire bails are inserted through holes in the ends of the frame's strap lugs and are retained by their own clip tension design. The bails also act as retainers for the lug ferrules.
   Non-geared tuning devices as used on violins, violas, cellos, lutes, older Flamenco guitars, and ukuleles are known as friction pegs, which hold the string to tension by way of friction caused by their tapered shape and by the string pull created by the tight string. 
  
  Section::::Construction and action.
   The image at right shows an isometric view of one style of mechanical snubber. When a disturbance occurs that exceeds the acceleration threshold of the snubber, the ball screw and drum produce angular momentum to the inertia mass. The inertial resistance of the mass engages the resilient capstan to tighten around a hardened mandrel, which is part of the structural tube. This, in turn, causes restraining force against the rotation of the ball screw. During standard operation, the associated acceleration is far below the threshold limit of the snubber and will not activate the capstan spring.
  
  Section::::Applications.
  
  Process Impulse Events
   Strip or paper cap guns use the aforementioned cap strip in lieu of the cap ring. As in the ring style of gun, each pull of the trigger advances the cap strip forward, pulls back the hammer to the point where it releases, striking the cap.
   Glazing jack
  
  A glazing jack or glazing machine is a type of machine used for polishing leather. The machine consists of a solid glass cylinder, typically around in diameter and in length, mounted to the end of a rotating or reciprocating arm. The arm repeatedly and rapidly draws the glass across the surface of the leather, with significant downward pressure, as the operator moves the leather underneath the arm.
   In the early years of the shipbuilding industry, workers covered their hats with pitch (tar), and set them in the sun to cure, a common practice for dock workers in constant danger of being hit on the head by objects dropped from ship decks.
  
  Management professor Peter Drucker credited writer Franz Kafka with developing the first civilian hard hat while employed at the Worker's Accident Insurance Institute for the Kingdom of Bohemia (1912), but this information is not supported by any document from his employer.
   The dome surround is made from a cloth that is coated with two types of resins and is folded to create creases that are tangent to the dome. This design holds the dome firmly, yet allows the dome to move accurately.
   Banjos usually employ a different mechanism using planetary gears - in this case the knob and the capstan both rotate on the same axis. A few guitars (e.g. the original Gibson Firebird, early Gibson basses and Mario Maccaferri's plastic instruments) have used this design.
  
  The guitarist adjusts the tension of the various strings using the knobs so that they are correctly tuned: a higher tension yields a sharper pitch, a lower tension a flatter pitch. Typical tensions for steel-string acoustic guitars with "light" tension strings are 10.5 kgf (23.3 lbf, 103 N) to 13.8 kgf (30.2 lbf, 135 N).
  
  Section::::Varieties.
   BULLET::::- 1997, "Zero reset mechanism". In 1997, A. Lange & Söhne introduced an advanced and elaborate self-winding movement: the Sax-0-Mat calibre features an integrated Zero-Reset mechanism that stops the balance when the crown is pulled and instantaneously moves the seconds hand to the zero position, much like in a chronograph.
   As long as the clove hitch can feed over the drum, the rope will feed through the device. In a fall, the drum is back driven by the rope as the device slides down the rope; when the drum rotation exceeds a certain angular velocity, it locks off to the frame and the increase in friction induced between the stationary drum and the rope causes the clove hitch to rapidly tighten around the locked drum to arrest the fall.
   Controls: The controls are generally simple and control the rotational velocity of the lap—the key control—and sometimes the direction of spin, i.e. clockwise or counterclockwise.
  
  Section::::Mast assembly.
  
  As stated above, the mast assembly is what makes a faceting machine a faceting machine. Its components are as follows:
   The term "locking" is much older, possibly originating with Grover, and refers to an "anti-backlash" design of the gears, which greatly reduced the slippage of the basic worm-and-gear system. The gear's teeth are shaped to lock into those of the worm, with the string tension insufficient to overcome the friction between the gears. Such a design is called self-locking. Grover Rotomatics and similar designs from other manufacturers are rightly called "locking tuners."
  
  Section::::Resistance to usage.
   Bl W, bridle wire, screwed into wippen, bent in the shape of a buckle at top to hold bridle.
  
  Bt, butt; or, more specifically, hammer butt. In some cheap actions the butt is joined to its flange "g", by the means described under the head of wippen flange; but in this action the center-pin is held firmly in the butt by a small strip of brass containing a set screw; somewhat obscure in the cut, but discernible. All center-pins turn in the flange and not in the middle part.
  
  HS, hammer shank in rest position.
   The method used to lock the drum against the device frame is by the use of two straight knurl edge discs that are thrown outwards by centrifugal force as they ride on parallel ramps milled into the drum's enclosed outer periphery. Two light return springs act as centrifugal force trips and as return springs to reset the discs when the fall load is released and the device is unlocked. A simple nylon guide is used to ensure both discs activate simultaneously to jam the discs between each drum ramp and the frame's lock ring.
   The first step in building a set of Swedish goggles is to construct a nose piece. Nose pieces can feature a variety of designs, some of the most popular are the included string threaded through the included rubber tube, a short length of the included strap (which is much more easily adjusted than the string), or simply using the string as a nose piece. For nose pieces using the string and tube, a pair of tweezers can be used to guide the string through the small holes located on the inside of the frames, as well as into the rubber tube. A small knot is then tied by hand and threaded into the tube. 
   The gag bit normally is used with two sets of reins; one on the bit ring that does not apply gag leverage, and the other on the small ring attached to the cord or rolled leather strap of the gag bridle cheekpiece. This allows for the bit to be used as a normal snaffle, with gag action used only when needed. Polo players, who must ride with the reins in one hand and cannot make instant fine adjustments, often use a gag bit with draw reins.
  
  Section::::Types.
  
  BULLET::::- Gag snaffle
  
  BULLET::::- Dutch gag
  
  BULLET::::- American gag or elevator
   In the liner lock, an "L"-shaped split in the liner allows part of the liner to move sideways from its resting position against the handle to the centre of the knife where it rests against the flat end of the tang. To disengage, this leaf spring is pushed so it again rests flush against the handle allowing the knife to rotate. A frame lock is functionally identical but instead of using a thin liner inside the handle material uses a thicker piece of metal as the handle and the same split in it allows a section of the frame to press against the tang.
   Doctoral hats are handmade, with the owner's head measured using a device called a conformateur. The hat rests on the top of the head. The typical price for the doctoral hat is around 500 euros.
   The AN-6530's frame is nickel-platedbrass and steel. Construction consists of stamped and milled pieces, soldered together. Milled brass pieces form the bridge and ferrule/strap lugs, and pieces of stamped sheet steel form the frame to hold the facepad and lenses. The ferrule / strap lugs are split lengthwise to facilitate removal and insertion of the lenses and rubber facepad. The lugs are secured closed by a salt-blued or parkerized and knurled carbon steel ferrule.
   An internal button ballnut employs a machined or cast button style return which allows balls to exit the raceway track and move one thread then reenter the raceway.
  
  An endcap return ballnut employs a cap on the end of the ball nut. The cap is machined to pick up balls out of the end of the nut and direct them down holes which are bored transversely down the ballnut. The complement cap on the other side of the nut directs balls back into the raceway.
   An S-nut, or S-style nut, is shaped like an "S". It is designed to clip on the edge of a sheet metal object. The threads are provided by an integrated nut.
  
  Section::::Types.:Square style.
   The Master of G series began in 1985 with the G-Shock II DW-5500C. This was a classic square case G-Shock watch, but the bezel contained softer parts and slipped over the buttons. This way Casio created a Mud Resistant structure. The DW-5500C was therefore nicknamed "Mudman". 
   The patent for this watch movement was applied in Switzerland on 1976, February 18. It was then applied in the USA on January 2, 1979 under the code US4132061A.
  
  The Abstract of the patent is :
  
  An extra-thin manually or automatically wound watch movement in which at least one wheel is pivoted in an overhang position by means of a single-race miniaturized ball bearing.
  
  Section::::Robert Annen and the ball bearing.
   Mattel produced an automatic firing cap weapon styled after the Thompson submachine gun. Pulling back on a slide, which simulated the charging handle of the real Thompson, prepared the gun for firing by tensioning a spring. When the trigger was pulled the spring power would drive the mechanism, firing a series of up to ten caps from a sprocket-fed roll. It was made initially for a Dick Tracy line of toys, then camouflaged for a Green Beret Guerilla Fighter line of weapons, then restyled again as a tie-in with the "Planet of the Apes" franchise.
  
  Section::::Types of caps.
  