An image of reproduction hourglass gauntlets, sold by the Medieval Shoppe in Parkes, NSW. The Medieval Shoppe produces and sells replicas of swords, shields, armour, and other historical weapons.
Their website provides some information about hourglass gauntlets (http://www.medievalshoppe.com.au/hourglass-gauntlets.html):
"When fighting was almost entirely hand-to-hand, the thorough protection of the hand was necessarily of paramount importance. Armour for the head and body was, after all, but a second line of defence against the attack which penetrated the guard of the weapon. Any damage to the hand which controlled all offensive movements, as well as all parries, would place a combatant at the mercy of his antagonist. But the armourer had not only to give his attention to the protective qualities of the covering which enclosed a part so vulnerable and so likely to receive a wound, he had also to consider how he should least interfere with the use of so complicated a piece of mechanism as the human hand. It was on account of these very important considerations that one finds the gauntlet always more complicated in the details of its construction than the rest of the protective outfit.
Underneath the plate was worn a leather glove, to the fingers and thumb of which small overlapping scales were attached to complete the defence of the hand. Hourglass gauntlets are considered the zenith of medieval gauntlets. An example of this type may be seen on the brass of Sir John de Saint Quintan in Brandesburton Church, Yorkshire, which may be dated at about 1397. The famous effigy of Edward, Prince of Wales, known as the Black Prince, in the cathedral church of Canterbury depicts this masterful warrior wearing this kind of hand defence."