Fasten climbing holds with allen screws and wooden screws. to find out suitable size of allen screw you have to put the screw throught the hole in climbing hold. If the screw sticks out on the board thickness you´re good. Internal thread of t-nut and external thread of allen screw must fully overlap. It´s wrong if threads meet partially or not at all.
When fasten holds you can freely rotate them. But be aware, do not force fastening screws, you can cause damage on the hold. To prevent rotation of holds during climbing use wooden screw.
More informations aboud instalation of climbing holds you can find here: “Instalation of Holds”.