Two different spike designs that can hold a pole from the inside (square shaped spike) or from the outside (round shaped spike). My volley ball net used cheap, soft plastic spikes to hold up the poles. I turned the design into something stronger and usable for different poles. It is strong enough to be hammered into the ground using a mallet. Great for backyard soil. Haven't tried umbrellas at the beach, but I assume it works the same. 

No special print settings except high infill and print laying on side for greatest strength. Use the scaling feature for different sized poles.