Off-topic a bit,, but a tin or aluminium plate would be light, cheap and easy to punch a hole through for a suspension point. They were very common in the 20th century.
Indeed, a metal plate is a very good match. They also described the object as silvery. If they knew it was an aluminum plate, describing it that way would make perfect sense.
There's an interesting aspect of the case that is often overlooked by those who are more inclined to believe than to search for the truth. It concerns the Trents as witnesses and whether they might have had a motive to hoax the photographs. In the Oregonian of June 10, 1950, Evelyn Trent is reported to have "
seen similar objects on the coast three different times, but no one would believe me".
In other words, Evelyn was already a repeat UFO observer when she and her husband allegedly saw the object come zooming toward their small farm. Paul also appears to have been well aware of the "flying saucer mystery" long before he took the photographs. Quoted in the Pasadena Independent of June 11, 1950, he said: "
I was kinda scared of it. You know, you hear so much talk about those things, and the government…"
To summarize, we have Evelyn, who believed she had seen flying saucers on several occasions, but whose friends did not believe her, and Paul, who had discussed the phenomenon and had heard a great deal about it. Witnesses like these must be considered in their proper context.
Evelyn may have seen "things" that she believed were flying saucers. It is obviously impossible to know what she actually saw, but the experience may have affected her deeply. If so, she would have carried that prior experience with her when the events of May 11 occurred.