I invented the mage gauntlet waaaaaaaaaaay back in 1983 - 30 years ago! It was later part of the loot from my adventyre 'The Island of the Gauntlet Mage' about the ruined fortress of a powerful magic user that mafe many unique gauntlet and glove items and spells. I referred to this as a 'metamagic item' when I first made it because of its function.
Mage Gauntlet: These are always found singly; 80% are for the left hand. Typically a mage gauntlet appears as a common leather glove for riding, but some (less than 10%) are either richly decorated with wmbroidery or resemble a battle gauntlet with metal plates over the knuckles (DM's choice). Whatever the appearance, the gauntlet has no effect on A.C., spellcasting, etc. A mage gauntlet will magically change size and shape to the fit the hand of any humanoid from halfling to ogre size. The gauntlet fits snugly and comfortably
The wearer of a mage gauntlet may wer three magical rings at the same time; two on the gauntleted hand and one upon the other hand.No more than one mage gauntlet may be worn at a time. Attempting to place more than two magical rings on the gauntlet will cause it to cease functioning for a full day (i.e., only one magical ring can be worn on the gauntlet during that time).