Go back and read my description of the two types of senders. The pictures of the senders you posted above and not bolts nor do they replace a bolt. Bolts hold two or more things together. The sender cannot do that as it is more of a plug than a bolt. I also do not see a water jacket plug on your motor so those senders must be used with a "Z" bracket. Now to head bolts. See the orange wire in the picture just above and to the left of the center spark plug? That is the temperature "switch" that triggers the over heat alarm. It is a switch (ON or OFF) and not a sender and would remain in place. Just to the right and slightly above that switch is the head of a bolt. That's a head bolt and there are six of them evenly spaced around each cylinder with a spark plug in the center of that bolt-circle. The head bolt just above and right of the temp switch would be removed and a "Z" - shaped bracket slipped over the bolt and bolt inserted again. The sender you show would then be screwed into the bracket so the end of the sender touches the cylinder head in the area close to the top spark plug. You would need the size sender that matches the threaded hole in the "Z" bracket. The "Z" bracket is also available from Faria or Teleflex. Just a heads up for future reference -- although your Bayliner has a Force outboard, all Bayliners do not. Boat builders have no idea what brand engine will be installed on them although some, like Bayliner did with certain models, have factory packages that included a trailer and engine. So when asking questions specific to the engine, 1988 Bayliner means nothing. You need the make and model of the engine to get meaningful responses. No offense intendend, but I sense a lack of mechanical and probably electrical skills so I again strongly suggest you obtain a service manual for your engine to avoid costly mistakes and to help you better understand your outboard engine.