When we export a smlx. from AS & import it into Revit the bolts lose the grip lengths. I have tried it in multiple Revit versions with the same results.
Autodesk has stated that this is the case and that the SMLX file does not carry the grip length information across.
They did provide a 'work around' though that would give you grips on the Revit side if "in the properties you uncheck the "Finish calculation at gap" and then once check and uncheck the "inverted" properties. This makes the grip length appear."

The work around works but when you have a frame with multiple bolts it becomes cumbersome.