Safety comment: this bracket is not designed to be load bearing (i.e. for someone to stand on this access point). If you need the access point to hold weight you will either need to reinforce the cover/bracket or use a different solution for your needs.

I wanted to create an access point for the spigot (faucet) under my deck and use the deck board as a cover plate. I designed the bracket, adjustable slider, and end piece in Tinkercad. The design is specific to the composite deck boards on my deck, which have three main grooves underneath. The bracket can likely be held in place well enough with either the slider or end piece alone, but I am using both as shown in the pictures. The fit of the end piece was snug, so I decided not to glue it in place. The slider provides some flexibility to more firmly adjust how much of the bracket is extended out for the deck board cover to rest on. I know these pieces will expand/contract with weather, so I will check it a few times during the year in different seasons. I live in the Midwest of the USA, so it will experience summer heat, winter freeze, humidity, and dryness. I used PETG for my prints and printed them on a X1-Carbon.

For the deck board being used as the cover plate, I cut a 1-inch (25mm) diameter hole to be able to pull the board up when accessing the spigot. I remixed a grommet design from Thingiverse to fit (see license txt file for original file info). I made two versions, one with the original flat cap and one with a more rounded cap (which is the one I printed and is shown in the pictures).