This neat kit is a keychain with a twist - well, more like a tweet. The whistle actually gives a quite loud shrill shriek. Uses a 7mm tube & is easily made with standard 7mm pen making accessories. The Chrome plating is ultra hard, gives a superb substrate adhesion, has a bright, attractive finish, and is stable and noncorrodable. It also gives ultra high metal-to-metal sliding wear resistance and provides superb abrasion resistance, even under high contact stresses. Plus it gives a very low wear rate (at least 100 times better than hardened steel or electroless nickel).