Double BTA spacerExtra spacers to convert a standard AeroGain BTA spacer or a Custom Mono Armrest to a double bottle system, These are only the spacers, and not the whole system. The hole distance underneath the spacers is 45 mm, so does not mount directly into an existing bottle mount. It is usually necessary to combine these spacers with a mount plate. For the whole system, please purchase the "AeroGain Double Bottle BTA system".