These bars are designed for hinged interior doors (with doorknobs), sliding glass or patio doors, and some window applications. Many models include removable or interchangeable top caps so the same bar can be used against a round doorknob or placed into a sliding-door track.
Listings describe heavy-duty metal construction, most commonly high-grade iron or high-grade steel. Some specify commercial-grade steel with measurements such as 1 mm (20-gauge) sheet metal; overall designs emphasize robust, rigid tubing and reinforced joints for strength.
Portable models fold, collapse, or telescope into a compact shape for easy storage in luggage or a bag. These compact, lightweight designs are intended for short-term use in hotels, rental properties, or offices and usually include a carry case or simple packing profile for travel.
Lengths vary by model. Examples from listings include approximately 18.25" to 47.50" (with one note that certain sliding-door caps reduce the usable maximum to about 46.50"), about 22" to 44" (with a listed maximum near 39.25" when door caps are used), and models that list separate ranges for hinged doors (~28.5"–45") and sliding doors (~25"–41.5"). Always confirm the usable range for your door type and whether included caps affect the maximum length.