BR6 Constant Temperature Heating Blocks for Microcentrifuge Tubes. These solid aluminum blocks are complete with their own heating element and thermoswitch. They have specially drilled holes that are conical on the bottom and cylindrical on the top. All other heating blocks being sold have holes that are cylindrical....correct for test tubes. With our unique holes, the microcentrifuge tubes are in contact with a heated surface for the entire immersed length. This will ensure that the tubes are heated quickly and evenly. There is no need to add sand, beads, water, etc. to get the proper heat transfer. The holes are drilled to hold 1.5 mL (1.7 mL) or .5 mL tubes. Temperature in the block is kept to ±1/2°C. and is fully adjustable from ambient to the maximum temperature shown in the table. If you are working at temperatures under 65°C, use Models A or E. If the temperature is between 65°C and 110°C, use Models B or F. All blocks hold 40 tubes. Models E and F have 20 holes for both 1.5 mL and .5 mL microcentrifuge tubes. For 120 volts, AC.