UN Thread Types. UN (Unified) is a specification of the shape and dimensions of the thread for a given size (diameter) of fastener and number of threads per inch of fastener length. UN bolts and machine screws are the type of fastener in everyday use in the US, UK, and Canada. UN, UNR, and UNJ thread dimensions are measured in Imperial units.
Causes The airway can become narrowed or blocked due to many causes, including: Allergic reactions in which the trachea or throat swell closed, including allergic reactions to a bee sting, peanuts, antibiotics (such as penicillin), and blood pressure medicines (such as ACE inhibitors) Chemical burns and reactions. Epiglottitis (infection of the structure separating the trachea from the esophagus)
Your trachea, or windpipe, is one part of your airway system. Airways are pipes that carry oxygen-rich air to your lungs. They also carry carbon dioxide, a waste gas, out of your lungs. When you inhale, air travels from your nose, through your larynx, and down your windpipe. The windpipe splits into two bronchi that enter your lungs. Problems with the trachea include narrowing, inflammation, and some inherited conditions. You may need a procedure called a tracheostomy to help you breathe if you have swallowing problems, or have conditions that affect coughing or block your airways.