Check the listing for details. Bullet Comparator/OGive Gauge (Tool Free) with 7 Sizes and Magnetic Base 🧲. Condition: New. Listed at 17.85 USD. Are you obsessed with precision and accuracy? Then an OGive comparator is a must for you. These fittings make it very simple to measure your OGive, no tools are required to setup or adjust the comparator. The piece that attaches to your calipers has a very strong magnet that will magnetize to your calipers. Each bushing is threaded, so when you need to measure the headspace of a different chamber, simply change the bushing by threading a new one on.The 7 bushings included are:22 (223/5.56)24 (243/6mm)25 (6.5 CM)2627 (270)28 (7mm)30 (308/7.62)This comparator is custom 3d printed with the highest quality PLA plastic. Very strong and very accurate in size.Does not include the calipers. To use this comparator, simply select the size you are reloading, thread it into the base. Attach the comparator to your calipers and zero the calipers with the jaws closed. Then measure your bullets and write down your results.