Review on Motion Pro 08-0013 Brass Carburetor Adapter: High-Quality 5mm x 0.8mm Adapter for Enhanced Performance by Luis Jacob

The downside is that this is not a machined solid piece of brass so the vacuum doesn't leak past the threads nut and o-ring. The defect is easily repaired by unscrewing the nut from the smooth end of the shaft just enough to put a drop of "red" (or blue, if that's all you have) Loctite on the exposed threads next to the smooth one applied at the end of the shaft. Then thread the nut back onto the Loctite and allow to dry before use. Now the O-ring can actually do its job and seal the surface between the nut face and the intake manifold mating face.