During the heyday of multiplex exhibition, 35mm trailers were produced on a massive scale and sent out to theaters indiscriminately. Trailers were supplied to theaters even when the venue did not plan to book the feature film being advertised. Trailers for an individual film were also supplied in multiple versions (scope, flat, green band, red band, etc.). As trailers had a finite shelf-life, there was no incentive for theaters to return them to distributors after their run.
The 1" trailer core was manufactured to facilitate the dissemination of 35mm trailers in the most cost-effective manner. Produced with a narrower exterior diameter than standard cores, the 1" trailer core allowed distributors to ship short quantities of film in the most compact way possible.
Trailer cores cannot be placed directly on a standard 5/16" rewind spindle for the purpose of film inspection. Trailer cores also do not fit on a standard split reel; they can only be used in conjunction with a trailer flange. Once the trailer core is seated on the trailer flange, the film can be wound onto a reel.
Most films trailers from the modern era were supplied to theaters on 1" trailer cores. Although trailer cores are perfectly acceptable for their original, short-term purpose, they are not recommended for archival storage. The 1" diameter of the core creates an overly tight wind, so it will cause curling and warping over time. This is particularly problematic for polyester, which is prone to base curl. Trailers should be transferred to standard 2" or 3" cores for long-term storage. If film has developed a significant curl from being stored on a 1" core, transferring it to a larger core and inverting the wind orientation can help reverse the curl over time.
When winding film off of a trailer core, the feed tension should be backed off considerably.