If you've ever messed with a rivnut, you know how frustrating it can be to install one, especially if you don't have a rivnut tool.
A trip to one of the big box hardware stores and less than $5 can get you this DIY rivnut tool.
Nothing special about the bolt (i.e. grade 8, etc).
Rivnut and tailgate spoiler screw kit: https://www.ebay.com/itm/New-GM-Tailgate-Spoiler-Mounting-Hardware-Kit-1999-2013-Chevy-Silverado-Sierra-/371681764982
Rivnut Link: https://www.amazon.com/GMC-General-Motors-NUT-11518684/dp/B008Y8MXQY/ref=pd_bxgy_263_2_encoding=UTF8&pd_rd_i=B008Y8MXQY&pd_rd_r=54G2FYDE156CHC0DYX35&pd_rd_w=sR0iE&pd_rd_wg=XOJ5G&psc=1&refRID=54G2FYDE156CHC0DYX35
Tailgate spoiler: https://www.1aauto.com/tailgate-spoiler/i/gmbtg00001f=863303&y=2005&utm_campaign=gb_csv_br&utm_content=BTG&gclid=EAIaIQobChMIqeugioaS2AIVnYWzCh0wgQL9EAQYByABEgJRaPD_BwE