ARP Rod Bolt Stretch Gauge

ARP stretch gauge, a high precision measuring tool for verifying preload on rod bolts, main cap bolts and other critical fasteners in a high performance engine. Measuring method recommended by ARP, more accurate than torque-only tightening.

Operating principle

The stretch gauge measures the exact length of a bolt prior to tightening, then monitors its elongation during installation. When the bolt has stretched the specified amount, the correct preload has been applied. This method is the most reliable as it eliminates the variations in friction inherent to torque-only tightening, and ensures proper clamping load regardless of lubricant used, thread condition or surface finish.

Common technical specifications

• Manufacturer: ARP (Automotive Racing Products)
• Origin: Made in USA (Santa Paula and Ventura, California)
• Type: Stretch gauge for rod bolts and fasteners
• Dial indicator: included in every kit
• Springs: extra heavy for consistent repetition
• Packaging: complete kit with insulated plastic carrying case

3 available models

• 100-9941 - Standard model: steel construction, black finish, dial indicator with 0.0005" (0.0127 mm) graduations, 0-0.0100" measurement range, red plastic carrying case
• 100-9942 - Billet model: black anodized billet aluminum construction, dial indicator with 0.0005" (0.0127 mm) graduations, 0-0.0100" measurement range, black plastic carrying case, improved ergonomics compared to standard model
• 100-9943 - Digital Billet model: black anodized billet aluminum construction, digital LCD readout with 0.0001" (0.00254 mm) graduations, maximum precision, plastic carrying case

ARP recommended usage

Measure each bolt length prior to installation. During tightening, monitor elongation and stop when the manufacturer-specified value is reached. Keep a log of pre/post lengths for each bolt. If after disassembly a bolt shows a permanent elongation of 0.001" (0.025 mm) or more, or any visible deformation, it must be replaced immediately.

ARP recommended tool for any professional engine builder who wants to guarantee accurate and reproducible preload on critical bolts of a high performance engine.