There are MK II fragmentation-type, modified military hand grenades available almost anywhere. They are inert but can be modified easily using readily available items. The body of the grenade is filled with shotgun or similar powder, a smoke grenade fuse is inserted in the threaded end, and a moly bolt is placed in the opposite end as a seal. Also, chemicals are available on the commercial market that, with paper mixtures, produce an excellent explosive. Recently, a Neo-Nazi was arrested when he sold an undercover police officer a 6-inch pipe bomb made from chemicals purchased at a drugstore. In another instance, what appeared to be an ordinary tube of caulking was a high-order explosive made commercially. An amount about the size of a marshmallow, used on a solid block of concrete 2-feet in diameter, left nothing but small pebbles after detonation. Frequently, terrorists use plastic explosives that only a trained eye will notice in an x-ray. Sentex, which is manufactured in Czechoslovakia, is common in Europe and is used by terrorists. An electronic switch called an E-cell is small and undetectable as an explosive timing device.