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A pinhole occluder is an opaque disk with one or more small holes through it, used by ophthalmologists, orthoptists and optometrists to test visual acuity. The occluder is a simple way to focus light, as in a pinhole camera, temporarily removing the effects of refractive errors such as myopia. Because light passes only through the center of the ...
An earlier patent covering both square-socket- and triangle-socket-drive wood screws, U.S. patent 161,390, was issued to Allan Cummings of New York City on March 30, 1875. As with other drive types conceived and patented in the 1860s through 1890s, it was not manufactured widely during its patent lifespan because of the difficulty and expense ...
Tamper-resistant versions with a pin in the recess are available. Metric sizes of the hex socket are defined by ISO 4762 (socket head cap screws), ISO 4026 (socket set screws with flat point), ISO 4027 (socket set screws with cone point), ISO 4028 (socket set screws with dog point), and ISO 4029 (socket set screws with cup point).
A set screw is generally a headless screw but can be any screw used to fix a rotating part to a shaft, such as a line shaft or countershaft. The set screw is driven through a threaded hole in the rotating part until it is tight against the shaft. The most often used type is the socket set screw, which is tightened or loosened with a hex key.
An occluder is placed over the eye that is not being tested (e.g.: over the left eye, to test the right eye's vision). A pinhole occluder is then placed before the patient's eye, and their vision is then tested again (each eye separately) to determine if the patient's poor visual acuity is a result of optical irregularities, or pathological issues.
In American English, a set screw is a screw that is used to secure an object, by pressure and/or friction, within or against another object, such as fixing a pulley or gear to a shaft. [ 1 ] [ 2 ] A set screw is normally used without a nut (which distinguishes it from a bolt ), being screwed instead in a threaded hole drilled in only one of the ...
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