Boston has an ordinance on blade length and carry, here it is.
Boston Municipal Code of Ordinances
16-45 PROHIBITING THE CARRYING OF KNIVES OR SIMILAR WEAPONS.
16-45.1 Carrying of Weapons Prohibited.
No person, except as provided by law, shall carry on his person, or carry under his control in a vehicle, any knife having any type of blade in excess of two and one-half (2½ ) inches, ice picks, dirks or similar weapons that are likely to penetrate through police officer's ballistic vests, or other object or tool so redesigned, fashioned, prepared or treated that the same may be used to inflict bodily harm or injury to another, except:
a. When actually engaged in hunting or fishing or any employment, trade or lawful recreational or culinary activity which customarily involves the carrying or use of any type of knife, or
b. In going directly to and/or returning directly from such activities, or
c. If the knife is being transported directly to or from a place of purchase, sharpening, or repair, and if packaged in such a manner as not to allow easy access to the knife while it is being transported.