These are a round pattern 1610 U-joint adapter, they are similar to the round 5 ton U-joint adapter only with a smaller OD. These are handy for fitting 1610 driveshafts on yokes with not alot of extra space.

Dimensions are listed below.

Series: 1610
Flange Or Swing Dia. In.: 6.875
Bolt Circle Dia. In.: 6.125
Bolt Hole Dia. In :.375 - DRILLED
Number Of Bolt Holes: 8
Pilot Dia. M=Male F=Female: 6.625 - MALE
Flange Face To C/L In.: 1.875
Outside Yoke Dimension In.: 5.312
Yoke Bearing Dimension In.: 1.875