We love the GG Equine Green Guard Diet Muzzle Insert because it is made from a soft, pliable, rubber-like material, that is non-toxic. It is secured into the bottom by pushing the insert tabs through matching slots* in the muzzle. Very secure once in place, these inserts can be removed but will take a bit of work to get out. But this is a good thing as it means your horse won't remove it before you do! The "diet" insert has 50% smaller holes to further restrict grazing. Reasons you may want to consider using an insert: Further reduce your horse's intake. Note that this insert is severely restrictive, so please make sure your horse is used to grazing without an insert before using. Protect your muzzle from excessive wear and prolong its life Have a softer material for your horse's grazing surface - the material is rubbery and softer than the muzzle itself. Sizes: Available in horse and pony muzzle sizes. CAUTION: Please ensure your horse is comfortable grazing in the GreenGuard muzzle prior to using inserts, especially the diet insert as it is extremely restrictive.