Collar of Natural Armor (3.5e Equipment)
From D&D Wiki
Collar of Natural Armor: This collar, usually crafted from bone or beast scales, toughens the creature’s body and flesh, giving him an enhancement bonus to his natural armor bonus of from +1 to +5, depending on the kind of collar. It is worn around a creatures neck. Can be used on a Familiar, a Druid's Animal Companion, or a Paladin's Mount.
Weak transmutation;CL 5th; Craft Wondrous Item, barkskin, creator’s caster level must be at least three times the collar’s bonus; Cost 1,000 gp and 80 exp(+1), 4,000 gp and 320 exp(+2), 9,000 gp and 720 exp(+3), 16,000 gp and 1,280 exp(+4), 25,000 gp and 2,000 exp(+5); Weight: - lb.; Market Price: 2,000 gp (+1), 8,000 gp (+2), 18,000 gp (+3), 32,000 gp (+4), or 50,000 gp (+5)