I googled "Landpride RCR1860 ", hit the landpride site and under "manuals" I got your mower in PDF format.
page 11 shows:
8. 802-277C BLADE BOL 1 1/8-12X3 7/16 W/KY
9. 803-020C NUT HEX 1/2-13 PLT
10. 803-036C NUT HEX JAM 1/2-13 PLT
11. 803-148C NUT HEX NYLOCK 5/8-11 PLT
12. 803-170C NUT HEX TOP LOCK 1 1/8-12 PLT.
Your bolt is a 1 1/8" deal.