The difference in profile
An L Type foundation bolt has a right-angle bend at the embedded end. A J Type has a curved hook. Both develop mechanical anchorage in concrete; the difference is in geometry, the space the bend occupies and how it sits relative to reinforcement.
How the choice is usually made
The structural designer selects the profile based on the tensile demand, foundation depth, concrete cover and the reinforcement congestion at the anchorage location.
- L Type is common where a compact right-angle bend fits cleanly within the pedestal
- J Type is used where a curved hook suits the reinforcement arrangement
- Where pull-out capacity governs, a plate anchor bolt is often specified instead
Manufacturing considerations
Whichever profile is specified, consistency across the batch matters more than the profile itself. Repeating foundation groups depend on bend dimensions, thread length and projection being identical bolt to bolt so that templates and base plates fit on site.