Analysis of information sources in references of the Wikipedia article "Clothespin" in English language version.
Use of frequency pins to identify the frequency in use. Pins, often clothespins, are marked with the color or channel number of the frequencies they represent. Only one pin is available at the flying site for each frequency. Transmitters shall not be operated without possession of a pin that identifies the frequency in use.
The first design that resembles the modern clothespin was patented in 1853 by David M. Smith, a prolific Vermont inventor.
