I am also using Shark Fin Antenna for my 2018 Honda Fit EX. The antenna base is very big. I have to take more area of the shark find base in order to make it fit. This is the one I got: https://www.amazon.com/dp/B01MYWV8F9/ref=cm_sw_r_cp_apa_i_FxokFbBFMM5H9 The red honda fit in the review are my pictures. It does come with 2 different antenna screws.
I use a shark fin antenna. I order it from amazon. https://www.amazon.com/dp/B01MYWV8F9/ref=cm_sw_r_cp_apa_i_rFc2EbBXRKCFS
For my 2018 Honda Fit EX after reading the manual I decided to installed the Shark Fin Antenna instead. 0 worries about the car wash. I use this: https://www.amazon.com/dp/B01MYWV8F9/ref=cm_sw_r_cp_apa_i_DIAuFbTHVQYBB