Concrete which is used in structural support of freeways, bridges, and large buildings, must be tested for anomalies. The testing equipment consists of probes which are inserted into testing tubes. The tubes are placed within rebar cages before concrete is poured. The prior art involved ad hoc methods of tying the tubes to the rebar. The improvement is pre-fabricated, mass produced cylindrical devices which can be axially snapped onto the testing tube. A first cylindrical device also has a perpendicular receptacle which facilitates connection to a second cylindrical device, where the second device can be axially snapped onto a piece of longitudinal rebar on the edge of the rebar cage. The combined first and second devices safely, accurately, and quickly affix the testing tubes to the rebar.