These sets have been put together for your ordering convenience, but you can mix and match other Starret test or back-plunger indicators and attachments with the No. 657A Magnetic Base and Swivel Post Assembly to suit your needs. Universal Back-Plunger Dial Indicators is one of the most versatile indicators available, and it is the "granddaddy" of them all. Over the years this tool has been improved by methods and materials but the basic design is unchanged. The design is older than most of you and has withstood the test of time and beaten all challengers because it is: Accurate and reliable, simple to operate, rugged, with few moving parts, smooth in operation, inexpensive-the best indicator value you can buy. Snug Complete PT18718 Post hole has a 5/16" diameter and 3/32-1/4" holding capacity. Can be used on our no. 252 height transfer gauge, nos. 57 and 257A and B surface gauges, on no. 657A magnetic base and swivel post assembly.