Definitely Siamese, native name is "Hawk". Mid Ayuthaya to early Rattanakosin (200-400 yo). The guard and blade shape indicated that the spear is footman's weapon. The square guard called "Chenk" should be loosely attached to the pole and can be freely rotated. But it 's possible to get ones are rusted or glued to the pole. The leaf-shaped blade was forged from a square bar. In your case, I noticed folded steel blade which indicates that the spear might be as old as mid-Ayuthaya period.
The pole made from specially cultivated Bamboo stick, which was carefully pruned for years. That means the bamboo was "born to be" a spear pole. This spear is a museum quality one and I 'm very glad that it is under posession of a good collector.
Heare are some similar spears.
http://www.wangdermpalace.com/exhibi..._stabbing.html
http://www.thailandmuseum.com/bangkok/rwutboran.htm
