but the idea of three nails being used to crucify Jesus is not from the Gospels
In the history of art, there was at the time-range from 13th - 16th cent. a change from 4 nails to 3 nails.
The early Christian art was afraid to represent the Passion or if they did so it was done in a manner which concealed the harsh reality. From the first centuries , there is not a single image of the crucifixion. The cross appears clearly only in the 5th century . Before this time, the cross in the catacombs was shown extremely rare . The representation of the crucifixion took place until the 12th century with four nails. In the following centuries three nails around the body allowed a more artistic movement and a position to make the believers more suffering in mention.
The idea was, to display a more un-natural way of being fixed to the pole and to express more suffering. The possibility to move , when being fixed with 3 nails, is much less then movements will happen by an attachment of 4 nails at each wrist and ankles.
Roman crucifixion was done, when nailed, with four nails ...
It (the victim) was then, as Plautus tells us, fastened with four nails to the wood of the cross (Lact., IV, 13; Senec., Vita beat., 19; Tert., Adv. Jud., x; Justus Lipsius De Cruce, II, vii; xli-ii).
Attached you will find some typical images in the change of the centuries ...