Microfluidic systems utilize connectors and tubing to transfer liquid to and from the sensor. Whether internal or external, these connectors can consist of luer and barbed ends. For more secure connections, threaded connectors for flangeless fittings are often preferred. When prototyping microfluidics or microfluidic instruments, using the correct hole size to tap the threads is critical for leak-proof connections with their corresponding flangeless connector. We compiled a quick-reference for flangeless fitting threads and the appropriate drill size. For instance, to make 1/4-28 threads, drill a hole with a diameter of 0.213 inches, then use the appropriate tap to make the threads.