Two Hole Pins ThreadedAll models are machine from hardened steel to make a very sturdy and lasting tool. We use double lead fast threads instead of ACME threads because they are as fast, if not faster, to screw on and more importantly, we have found that ACME threads tend to loosen, and dont hold job as secure as our double lead fast threads. Models 42050 TM, 42050 T and 42050 TL have one pin that has a 360 vial for easier vertical leveling that just snap in and out for