Hand tool having an adjustable head with joint lock mechanism

1. A hand tool having an adjustable head with a joint lock mechanism, comprising:

a head having a rear end, the rear end having a convex pivotal portion;

a handle having a front end, the front end having a concave pivotal portion pivotally coupled to the convex pivotal portion of the rear end of the head, the handle having a first aperture longitudinally extending from the front end thereof, and a second aperture perpendicularly intersecting the first aperture;

a fastening device disposed through the convex pivotal portion and the concave pivotal portion such that the fastening device is pivotally coupled to the convex pivotal portion while being fixedly coupled to the concave pivotal portion; and

the joint lock mechanism being disposed between the rear end of the head and the front end of the handle;

the joint lock mechanism comprising:

a first engaging device disposed at the rear end of the head, the first engaging device having a plurality of slots spaced equidistantly along the surface of the convex pivot portion;

a second engaging device received in the first aperture of the front end of the handle, the second engaging device having a front end and a rear end, and the second engaging device having at least one engaging portion formed at the front end thereof;

a pull button having a knob portion and an engaging portion beneath the knob portion, the engaging portion extending along the second aperture and engaging the second engaging device;

a first elastic device received in the first aperture and abutting against the second engaging device with a forward force such that the front end of the second engaging device is pushed to engage the first engaging device; and

a positioning device having a positioning element and a second elastic device, the positioning element being disposed at the front end of the first aperture and having a shape substantially matching that of the engaging portion of the second engaging device so as to guide the engaging portion of the second engaging device to engage one of the plurality of slots; the second elastic device being positioned behind the positioning element and abutting against the positioning element with a forward force.

2. The hand tool according to claim 1 , wherein the first aperture has a front portion having a larger diameter and a rear portion having a smaller diameter which forms a shoulder portion in between, and the second elastic device is disposed in the front portion with its front end abutting against the positioning device while its rear end abuts against the shoulder portion.

3. The hand tool according to claim 1 , wherein the second engaging device includes a pair of slots formed at opposite sides between the front and the rear ends thereof, and the engaging portion of the pull button comprises two hooks engaging the corresponding pair of slots such that the pull button is adapted to actuate the second engaging device to move along the first aperture.

4. The hand tool according to claim 1 , wherein the second engaging portion has a through slot formed between the front and the rear ends thereof, and the engaging portion of the pull button is a hook for engaging the through slot such that the pull button is adapted to actuate the second engaging device to move along the first aperture.

5. The hand tool according to claim 1 , wherein the surface of the convex pivot portion is an arc.

6. The hand tool according to claim 1 , wherein the knob portion has a surface formed with a plurality of anti-slip teeth.

7. The hand tool according to claim 1 , wherein the knob portion has a surface formed with pattern consisting of a word “LOCK”, a mark at the side of the head and a double arrow crossing said mark.