"Titanium has become a preferred material for Orthopedic implants over the past 10-15 years because of a number of its inherent properties. It is inert in the body, and has sufficient strength to support the mechanical loads (assuming proper design and size of the implant). It is also very resistant to fatigue failure - that is, it can undergo many (millions) of cycles of mechanical loading without failure - a property that is extremely important in an Orthopedic implant that will be subjected to a million cycles of loading a year. Most Orthopedic titanium implants are actually an alloy of titanium with small amounts of aluminum and vanadium, as pure titanium implants are somewhat brittle and have a higher rate of fracture. Titanium alloy is less brittle, and holds up quite well."
"As to why the implants you have are not in someone's body, they are not defective; they were actually in the operating room and taken out of their sterile packaging in anticipation of being implanted, but were for one reason or another not used. In some cases, the devices were implanted, but found to be too long or too short, and were then replaced with a correct sized implant. We are not allowed to re-use devices that have been implanted and removed, as there is no feasible way to ensure that the stresses of implantation have not altered the mechanical properties of the device. So they become very expensive junk. (Any implant that was removed from a patient was thoroughly cleaned and then sterilized before it left the OR). Other devices may have been removed from their packaging, but not implanted because the surgeon changed his/her mind about the size or decided to use a slightly different implant before actually putting in the patient. Depending on the implant, re-sterilization in the hospital may not be practicable - more expensive junk."
"These intramedullary rods or nails are placed inside the intramedullary canal (marrow cavity) of long bones like the femur or tibia to stabilize fractures of these bones until they heal."

The titanium coins were minted for Gibraltar by the Pobjoy Mint in the UK. Only 2001 of them were produced, and I think they have kind of given up on making more titanium coins because the hardness of the metal makes it very difficult to work with, not to mention how quickly it destroys the dies. They did issue one other Five Pound coin in the year 2000, this one to commemorate the famous "Tuppenny Blue" postage stamp, which is currently valued at $800,000. I think they were already committed to minting the second coin before they figured out what a pain it would be to produce coins from titanium.

I read through your page covering Titanium. You'd mentioned that you were unsure why anyone would want a titanium crowbar, however there actually is a market for such an item, although the market is a bit obscure. Titanium crowbars are often used by SCUBA divers for wreck diving or salvage. The reason a crowbar would be needed is obvious, and like you said, a titanium crowbar won't rust. However, more important than its resistance to rust, is its density.

Short story:
Divers that need a crowbar underwater would be safer and more comfortable with a titanium crowbar.

Long story:
The weight of a regular crowbar would cause the diver to either be overweight while diving, or require that the diver wear less weight in their weightbelt to maintain proper buoyancy. Part of diving is the eternal struggle for buoyancy. Because of this, divers have to have a measured amount of lead weights attached to them to assist them in staying submerged. These weights assist at first, but eventually become unnecessary due to the increasing amount of water directly above the diver. To balance the weights at lower depths, the diver must use a BC (Buoyancy Compensator), which is a vest that they can inflate or deflate to modify their displacement, and therefore allow them to "hover" in the water. If the diver chooses to be overweight, they would descend more rapidly, and find it necessary to keep their BC inflated significantly more. If the diver accidentally dropped the crowbar, they would ascend and find it necessary to deflate their BC rapidly to keep from ascending too fast. The more underweight the diver, the faster they would ascend.

A regular crowbar would not only serve as more weight attached to the diver, but it's also off center when it's used. This means that a diver who starts using a regular crowbar would most likely become inverted as it moved away from the body, requiring deflation of the BC to compensate, or inflation as you bring it closer to your body. This would make it very difficult to use effectively.

Therefore wreck and salvage divers prefer a lighter, less dense crowbar, with equal or greater strength of a regular crowbar, for the reasons of safety and convenience. Oh yeah, and it doesn't rust!

When rock climbers lay out new routes up cliffs there will often be rocks and handholds (sometimes relatively large, i.e. perhaps a hundred pounds or so) which are not securely attached. These rocks pose a real danger for climbers. If you find yourself hanging from one of these guys and it suddenly shifts or lets go, not only is the climber in danger - a moving rock may damage a rope easily - but especially those on the ground may be hurt. The more vertical the surface is the more danger these rocks may pose, and if you are climbing a roof, i.e. a severely overhanging climb, these rocks may peel off at any time. Just hope that you are not anchored in to it when it goes!

What you need is a very light crowbar; light enough to climb with it clipped onto your harness, and strong enough that you can give a really good crank to any suspicious rocks in order to drop those that are not secure. Of course this is only done during the initial route set up. Once the route has been cleaned, it should be safe for future climbers and spectators, but for the early ascents, a titanium crowbar is so much nicer than a steel one.

I work for a defense contractor, and last year had a project that involved temporarily installing some equipment on a Navy vessel. For various technical, administrative, and warfighting reasons, we attached the various equipment elements to the overhead and bulkheads with extremely strong neodymium magnets (strong enough to crush the fingers of inattentive persons, and requiring heavy shielding to transport).

A titanium crowbar with a specially ground and polished edge was the tool that at allowed us to have an installation that was virtually permanent, yet could be repositioned or removed at will. When a device needed to be moved, one engineer would use the crowbar to lever the magnet loose from the ship, while another (wearing heavy leather gloves) would grab the equipment and pull against the magnetic force. Without the titanium crowbar, those magnets would be stuck in place forever.

Respectfully submitted,
-Jeff Jennings.

No. Actually, the difference between a bolt and screw is based on its application, not appearance. A bolt is used with a nut to produce a clamping force to hold materials together; whereas a screw interlocks threads with the material itself (no nut on the end).

Screws usually have threads all the way up to provide the maximum possible thread-to-thread contact area with the material for maximum holding power. Bolts usually have only enough threads at the tip to attach a nut. But, some bolts also have threads all the way up so that one or more nuts can be installed anywhere.

A screw is perfectly adequate against smaller forces. Humans and machines can easily install screws (no fumbling with a nut). Without a nut, that's one less part to stock and pay for, and one less part to fall off or become lost. Given the large number used, the savings in cost and efficiency make screws an effective solution.

However, against greater forces, the threads in the material are likely to fail and the screw would rip out. Thicker and stronger material would be required to produce strong-enough threads in the material to resist these greater forces. But that would be heavier and more expensive. Instead, a thick, strong nut can be installed to rely on the nut's threads instead of the material's threads. With a nut and a bolt you can use relatively weaker and thinner (usually lighter and less expensive) material.

Your observation that a bolt usually has a hex head or other external-drive is simply because that type of head allows greater force to be applied, which is necessary to achieve the purpose of a bolt. On the other hand, the head of a screw (slotted, Phillips, internal drive) is designed for convenience of installing and removing, rather than great forces. In fact, most screw heads are purposely designed to be torque limiting (the tool slips out) to prevent over-tightening.

In summary, although you may be able to guess at the manufacturer's intended application based on the appearance of the fastener, a bolt or screw is not defined by its appearance, but in how it is used. You can use most screws as bolts, simply by adding nut on the end, and most bolts as screws, simply by tapping (adding threads to) the material.

The nearest analogy I can think of is to select a knife and ask "Is it a kitchen utensil or a weapon?" The manufacturer probably had a particular purpose in mind, and there are certain visible features that would suggest a particular knife is better suited for one application over the other, but what you call it depends on how it is being used.

Hi. I noticed that your Aeschynite sample is from Iveland in Norway. The small community of Iveland is actually famous for their mines and minerals. Here's a folder with some information about a local exhibition. They also have at least 5 mines that are open to the public for a small price, where you can dig for minerals yourself.