Thread Pitch & Specification Guide
Restoring a vintage steel frame requires absolute mechanical precision. Use our verified workshop specifications to identify French, Italian, and British threading standards before selecting your spares.
British (BSA)
Italian Standard
French Vintage
The modern standard. Left-hand thread on the drive side, right-hand on the non-drive side. Shell width is typically 68mm with a 1.37" x 24 TPI pitch.
Right-hand thread on both sides. Requires regular torque checks to prevent self-loosening. Shell width is 70mm with a 36mm x 24 TPI pitch.
Right-hand thread on both sides. Found on classic steel frames prior to 1980. Shell width is 68mm with a 25mm x 1mm metric pitch.
Identify Your Threading
Follow these three mechanical steps to determine your frame specifications. Accurate measurement prevents thread damage and ensures component longevity.
01. Measure Shell Width
Use a vernier caliper to measure the bottom bracket shell width. Standard steel frames measure exactly 68mm, 70mm, or 73mm.
02. Verify Thread Direction
Examine the drive-side threads. If they tighten counter-clockwise, you have a British BSA frame. If they tighten clockwise, it is French or Italian.
03. Check Inner Diameter
Measure the internal diameter of the shell. British measures 33.7mm, Italian measures 34.8mm, and French measures 34.6mm.
Standard Frame Specifications
A comprehensive reference for vintage restoration and touring setups. These exact dimensions ensure compatibility with our mechanical spares.
Bottom Brackets
Headset Standards
Rear Hub Spacing
BSA uses 1.37" x 24 TPI with a 34.8mm diameter. Italian uses 36mm x 24 TPI with a 36mm diameter. French uses 25mm x 1mm metric pitch.
ISO standard headsets feature 1" x 24 TPI threads. Vintage French headsets use a 25mm x 1mm metric thread, requiring specific restoration-grade components.
Vintage steel frames typically feature 120mm spacing for 5-speed hubs, 126mm for 6-speed hubs, and 130mm or 135mm for modern touring wheelsets.
Verify Your Specifications
Unsure about your thread pitch or frame compatibility? Speak directly with a mechanical specialist at our Bristol workshop to confirm your measurements before ordering.