Plastic seals Variable length seals, commonly called "pull tight seals" can fit many applications from securing the neck of a bag or mail sack to sealing chemical drums, first aid kits and fire extinguishers. They have an adjustable length much like a cable tie but offer a much higher security level and an audit trail due to sequential numbering and the ability on some seals to be bar-coded and have a company name and logo printed or laser etched on.
Fixed-length seals tend to be more tamper resistant than variable length as there are no sliding parts, they simply 'click' into place to lock, which can make them easier to fit than variable length seals. Most fixed length seals can also be branded and numbered for extra security. Fixed length is often the choice of single use security seals for transport applications.
Padlock seals are usually supplied as a completely plastic seal, shaped as a standard padlock would be. Technically, they can be classed as a fixed length seal. They feature the same types of tamper-evident protection as variable length and fixed length have available - numbering, bar-coding and branding - but fit some different applications. The most common use for these seals is for airline duty-free trolleys. One reason for this is that plastic padlocks can be placed over a locking part as any metal padlock would be to secure, but do not require keys to open, they simply break off at their built in break point using hands or a small pair of wire cutters. They are secure due to the audit trail available as a result of the sequential numbering.
Meter seals are used with electric or gas or water meters and usually molded in polycarbonate. The transparent body of the seal means that the locking mechanism is visible, and can provide clear indication of tampering. Meter seals can withstand exposure to sunlight and extreme weather, and a wide range of temperatures. Designed for only a single use, they are destroyed when removed. Some meter seals contain components which glow under ultraviolet light, allowing the seal to be easily located in darkness.