According to ASTM F1554-07a when Grade 36 is specified, a weldable Grade 55 may be furnished at the supplier’s option.

Portland Bolt may use this substitution in situations when it will save the customer time and/or money. This allowance is useful for Portland Bolt when asked to supply Heavy Hex Grade 36 bolts because we stock “blanks” that are already headed with a Heavy Hex head in F1554 Grade 55. Since the “blanks” meets S1 of F1554 (weldable) we are allowed to provide Grade 55 instead of Grade 36 to meet the specified head style.

Please note that this substitution of weldable Grade 55 for Grade 36 is the only substitution of a higher strength bolt for a lower strength bolt that ASTM allows within the context of their fastener specifications. Except for this instance, Portland Bolt estimators will never suggest you substitute one grade of fastener for another grade or suggest you substitute one type of bolt for another type of bolt without first consulting with the Engineer of Record.