POWERTEC 1/8, 3/16, 1/4, 5/16, 3/8, 7/16, 1/2 in. Steel Drill Bit Stop Collar with Split Ring Design and Size Markings (Set of 7) 71491 - The Home Depot
SledgeHammer Oil Tools Pvt. Ltd.
Drixet Drill Stop Bit Collar Set – Kit Includes: 1/8", 3/16”, 1/4”, 5/16”, 3/8”, 7/16” and 1/2-Inch with Allen Wrench to Tighten The Stops Set-Screws (7-Piece) - Amazon.com
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Stop Collar Manufacturers - China Stop Collar Factory & Suppliers