Thanks Al, it should indeed be a metal throated platic scabbard, not a metal one.
Older Than Dirt, please don't be offended, if your friend's US bayonet has a steel scabbard, it is the wrong one, length makes no difference. The US hadn't used a steel scabbard since the time of the Krag bayonet. We would need a photo of what he has to assure that we can give you proper information to help him. Barring that, for accurate information on the correct scabbard for the bayonet see:
Bayo Points 6
An excellent article by Gary Cunningham showing the development of the M3 and M7 US Scabbards for the M1905, the M1905E1 (Shortened M1905) and the M1bayonets and the M8 scabbard used for the M1 Carbine bayonets and later models for other US rifles..