Princebabe, just contact the people you ordered the pins from and tell them to send you the correct 1/8 inch size. Pins designed to shear are tempered to have a specific breaking point, to protect your prop and motor shaft. Substituting some random stainless, which is not the proper temper, and therefore may not break at the correct force, means something else will. Either your prop, or your motor shaft. Motorguide,or any other maker will not warranty anything damaged by using incorrect parts. Just saying.

Take your motor with you to Ace Hardware. You have the wrong Shear pin diameter. The proper Shear pin will freely go into the Shaft hole where it is stainless. You simply need a little smaller OD ( outside Diameter ) pin. Once properly installed the pin can move a millimeter or 2 (its metric). The retaining nut on propeller will keep propeller and pin in place. You need to have the hole on prop shaft setting horizontal ( open towards 9 and open towards 3 on a clock ) then install the pin. Center the pin. Install the propeller ....do not let the prop shaft turn until the propeller nut ( black with brass threads in your pictures ) is tight. The proper shear pin will only be long enough to go through prop shaft but allow propeller to seat when nut is tightened. Once you get proper pin part number get a spare and then show all of us the proper pin that must of been misplaced or never sent with the set up you purchased.

I would figure there may be a mistake on which pins were sent to you or something. If it is new and you purchased it form a retailer within last 90 days you should notify the retailer. Most warranties will be from Manufacturer. Hopefully you purchased it new. There should be information with the product to call or notify Manufacturer. If the the shear pins sent are simply too large of OD ( outside diameter ) as compared to the hole or mounting plate or ID ( inside Diameter ) then they can just send you the proper size pins for the application you purchased. Start Googling the model and make etc. with shear pins in the search and maybe you can find out more that way too.

If there is only one size for all models and years. The pin could be bent or the hole needs to be drilled to same size. Many pins like shear pins are pressed in to proper position meaning it takes constant pressure to get them in proper position. They when they are pressed in it is so they stay in proper position.