Snug, Two 1/4" (6.3mm) diameter holes. Adapts 196, 650, and 651 Series Dial Indicators and 657Y Indicator Attachment to 657X Rod. Two 1/4" (6.3mm) diameter holes. Adapts 196, 650, and 651 Series Dial Indicators and 657Y Indicator Attachment to 657X Rod. Snug (Sleeve).