Reddit reviews uxcell a15071400ux0035 M4x12mmx1 mm Stainless Steel Round Flat Washer for Bolt Screw Pack of 100

Here's a couple more little bits of advice if you decide to stick with the Tarantula...

Order a pack of these t nuts. Unlike the T nuts that come with the kit, you pop them into the rails and they hold themselves in place (although you can slide to line stuff up). It makes assembly much easier. With the stock T nuts it can be hard to get them all lined up when you need to attach a part to the extrusion. And then you never really know if they engaged the extrusion or not. With those other ones, you put them in the extrusion and the hold the part up and start the screws. They almost can't be done wrong - if they're in the channel, they will be properly engaged with the extrusion. You can sometimes accidentally knock them crooked in the channel, but when it happens you know it and it is much easier to fix than problems with the stock t-nuts because taking the part off doesn't mean you have to redo all the T nuts associated with that part.

Order a pack of larger O.D. 4mm washers and put them on any nut/bolt that faces up to the acrylic or even printed plastic parts. Helps prevent damage.