FORUM RULES UPDATED - The forum rules have been updated to continue to provide a friendly and safe environment for our member community. Please take a moment to review the updated rules and our terms of use and privacy policy. Click here for Forum Rules which has links to the 'terms of use' and 'privacy policy'.
Looks like a red plastic plug used to plug a hole in something to keep it clean till it was installed. Nothing on your engine that I recall uses a plugged hole like that. Could be from something other than engine that was installed in the engine compartment.
Ayuh,... Looks like a 3/8"- 1/2" port/ pipe plug/ cover... I've got a toolbox full of 'em....
Like Don said,... It's Throw-Away shipping packaging.....