American Gage Design Specifications (AGD)

AGD specifications were developed in 1945 at the request of the U.S. Commerce Department through the National Bureau of Standards - now the National Institute of Standards and Technology (N.I.S.T.).  These specifications provide the dimensions to allow interchangeability between indicators of different manufacturers in fixturing.  As you will see, these dimensions pertain to sizes for space consideration and for holding.

There are two major differences between American Gage Design and other specifications. The first is the stem diameter. AGD specifies .375" (9.5mm) and some other standeards spedify an 8mm (.315") diameter. International specifications allow for either one.  The .375" (9.5mm) diameter provides a little more protection for the rack when clamped on the stem but 8mm diameters are available also.  The other difference is the contact thread. AGD specifies a #4-48 thread. Other standards specify a metric thread, #M2.5.

The AGD Design Specifications:

  Size Group Min.Diameter-In. Min.Diameter-mm Max.Diameter-In. Max.Diameter-mm
  0 1" 25mm 1 3/8"  35mm
  1 1 3/8" 35mm 2" 50mm
AGD 2 2" 50mm 2 3/8" 60mm
  3 2 3/8" 60mm 3" 75mm
  4 3" 76mm 3 3/4" 95mm

AGD specifies 2 1/2 turn indicators to cover any particular range.  The reason for this is that in an effort to get the most out of the indicator, the operator "loads" it to about 1 1/3 turns and sets zero on his master.  The indicator will now show the accurate deviation for a full revolution, plus or minus.