A sickle cutting apparatus comprising: a frame structure arranged for forward travel over ground having a standing crop thereon; a cutter bar secured to the frame structure and extending transversely across a front end of said frame structure; a plurality of stationary knife guards mounted along the cutter bar and each knife guard including at least one finger projecting forwardly therefrom; each guard finger having an upwardly facing ledger surface with opposed side edges thereof arranged to provide first and second shearing edges; a sickle bar mounted in transversely extending position and being driven for reciprocating movement relative to said guard fingers; the sickle bar having a plurality of knife blades mounted thereon for movement therewith; each of the knife blades having a rear plate portion for mounting on the sickle bar and at least one forwardly extending blade portion; each of the blade portions having a cutting surface for passing across the knife guard fingers; each of the blade portions having on first and second sides first and second side cutting edges (23C, 23D) to cooperate with shearing edges of said guard fingers; a plurality of hold-down members each having a rear mounting section mounted at the cutter bar and each including at least one forwardly extending hold-down element for engaging an upper surface of a knife blade as it passes the hold-down element to hold down the knife blades onto the ledger surfaces of the guard fingers; each of the rear plate portions having at least one hole for cooperating with a mating hole in the sickle bar for receiving through the plate portion and the sickle bar a mounting fastener; characterized in that each hole is connected to an associated slot extending rearwardly in the rear plate portion from the hole to a rear edge of the rear plate portion to allow the knife blade to slide forwardly until the knife blade is released. a frame structure arranged for forward travel over ground having a standing crop thereon; a cutter bar secured to the frame structure and extending transversely across a front end of said frame structure; a plurality of stationary knife guards mounted along the cutter bar and each knife guard including at least one finger projecting forwardly therefrom; each guard finger having an upwardly facing ledger surface with opposed side edges thereof arranged to provide first and second shearing edges; a sickle bar mounted in transversely extending position and being driven for reciprocating movement relative to said guard fingers; the sickle bar having a plurality of knife blades mounted thereon for movement therewith; each of the knife blades having a rear plate portion for mounting on the sickle bar and at least one forwardly extending blade portion; each of the blade portions having a cutting surface for passing across the knife guard fingers; each of the blade portions having on first and second sides first and second side cutting edges (23C, 23D) to cooperate with shearing edges of said guard fingers; a plurality of hold-down members each having a rear mounting section mounted at the cutter bar and each including at least one forwardly extending hold-down element for engaging an upper surface of a knife blade as it passes the hold-down element to hold down the knife blades onto the ledger surfaces of the guard fingers; each of the rear plate portions having at least one hole for cooperating with a mating hole in the sickle bar for receiving through the plate portion and the sickle bar a mounting fastener; characterized in that each hole is connected to an associated slot extending rearwardly in the rear plate portion from the hole to a rear edge of the rear plate portion to allow the knife blade to slide forwardly until the knife blade is released.