Lathe threading inserts use and direction IR IL ER EL

Is there a difference between an external left hand threading insert, and an internal right hand insert?
Same goes for external right and internal left.

Can an ER insert fit an IR holder? Same question for EL insert in IL holder.

Thanks.

Internal and external threads have different depths at the same pitch which might not matter much, but rake/clearance angles make a difference.
Check the tool catalog or ask your dealer if a given insert might have all the same specs.

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