It is a centre cap or literally a hub cap (although most people now seem to think of wheel covers when the term "hubcap" is used).
I note that the page J Mac linked uses the terms "snap" (snaps on from the outside) and "push" or "push thru" (goes into the wheel from the inside before mounting the wheel. In either case, a cover like this for just the centre bore does not need to be removed for access to the wheel nuts. I have automotive wheels that I have mounted and dismounted seasonally for years and never touched the cap.
As that supplier's page suggests, the key dimension to determine what fits is the centre bore size (the diameter of the whole in the wheel, or "pilot hole" size). Since typical trailer wheels don't locate on the centre bore, that hole can be any size as long as it is big enough to clear the hub, so you need to check your specific wheels. If the spare is the same wheel (often a vehicle with fancy alloy wheels will have a plain steel spare) then I would measure that one, or even take it to a wheel/tire store or trailer supply store to test fit a replacement.
Originally Posted by cpaharley2008
Chrome/aluminum/shiny, I'm not sure, they are not the white ones is all I know.
Shiny wheels can be plated with shiny metal (such as chrome) or made of metal which can reasonably be polished (typically an alloy of aluminum). Chrome plating can be put on steel or aluminum alloy wheels, but traditionally when people said "chrome wheels" they meant chrome-plated steel wheels. The optional wheels that I have seen in Escape photos and on Escape trailers are all polished aluminum alloy, usually just called "alloy". The hub cap in these appears to be chrome-plated plastic or steel - if it's dented, it's presumably steel; if cracked, it's presumably plastic.
Looking at the 15" trailer wheels with 5x4.5" bolt pattern offered by eTrailer
, it looks like there is some variation in bore (or "pilot hole") diameter, but most are 3.19".