The majority of those threads are 1/4-20 or some metric near equivalent. The suggestion to get different screws and try them in the holes is good. The "dash 20" or dash with another number is how many threads per inch there are. A 1/4-20 screw or threaded insert has 20 threads per inch.
Monitor Audio Silver RX6 Spike Thread size?
Anyone know the spike thread size for this speaker. I bought a used pair and the spikes were missing. Thanks!