Impact tool

1. An impact tool comprising:

a motor;

a hammer that is rotated by the motor;

an anvil configured to be struck by the hammer to rotate the anvil about a rotational axis, the anvil having an outer circumferential surface;

a hammer case that houses the hammer; and

at least two hearings disposed inside the hammer case and mounted upon and around the outer circumferential surface of the anvil so as to rotatably couple the anvil with the hammer case;

wherein the beatings are of differing types and/or have differing inner diameters and/or differing outer diameters.

2. The impact tool according to claim 1 , wherein the hearings have differing inner diameters and/or differing outer diameters.

3. The impact tool according to claim 2 , wherein the diameters differ by more than 5%.

4. The impact tool according to claim 3 , wherein the bearings are held by the hammer case.

5. The impact tool according to claim 3 , wherein the hearings are held by the anvil.

6. The impact tool according to claim 1 , wherein:

one of the bearings is one of a regular ball bearing, an angular contact ball bearing, a self-aligning hearing and a plain bushing; and

another one of the bearings is a different one of a regular ball bearing, an angular contact ball bearing, a self-aligning bearing and a plain bushing.

7. The impact tool according to claim 6 , further comprising:

an intermediate washer interposed between the regular ball bearing and the angular contact bearing.

8. The impact tool according to claim 7 , wherein:

the anvil has an insertion hole having a regular hexagonal shape in transverse cross section and into which a bit (B) is inserted; and

a spacing (S) between diametrically-opposing flats on an inner surface of the insertion hole is set to a dimension such that a hex gage, whose across-flats-distance dimension is 6.35-6.34 mm, is fully insertable into the insertion hole, and a hex gage, whose across-flats-distance dimension is 6.37-6.36 mm, is insertable only up to a depth that is less than 5.4 ram from the opening of the insertion hole.

9. The impact tool according to claim 8 , further comprising:

a contact member disposed inside the insertion hole of the anvil and configured to radially and/or axially abut a bit inserted into the insertion hole.

10. The impact tool according to claim 1 , further comprising:

a contact member disposed inside the insertion hole of the anvil and configured to radially and/or axially abut a rearward end of a bit inserted into the insertion hole.

11. The impact tool according to claim 1 , further comprising:

at least one intermediate washer interposed between and directly contacting two of the bearings.

12. An impact tool comprising:

a motor;

a hammer that is rotated by the motor;

an anvil configured to be struck by the hammer to rotate the anvil about a rotational axis, the anvil having an insertion hole, which has a regular hexagonal shape in transverse cross section and into which a bit is inserted; and

a hammer case that houses the hammer;

wherein a spacing (S) between diametrically-opposing flats on an inner surface of the insertion hole is set to a dimension such that a hex gage, whose across-flats-distance dimension is 6.35-6.34 mm, is fully insertable into the insertion hole, and a hex gage, whose across-flats-distance dimension is 6.37-6.36 mm, is insertable only up to a depth that is less than 5.4 mm from the opening of the insertion hole.

13. The impact tool according to claim 12 , wherein the spacing (S) between the diametrically-opposing flats is set to a dimension such that a hex gage, whose across-flats-distance dimension is 6.39-6.38 mm, is not insertable through the opening of the insertion hole.

14. An impact tool comprising:

a motor;

a hammer that is rotated by the motor;

a bit;

an anvil configured to be struck by the hammer to rotate the anvil about a rotational axis, the anvil having a ball that holds the bit inside an insertion hole of the anvil, the insertion hole having a regular hexagonal shape in transverse cross section;

a hammer case that houses the hammer; and

a contact member disposed inside the insertion hole rearward of the ball and abutting the inserted bit in a radial direction or an axial direction of the inserted bit.

15. The impact tool according to claim 14 , wherein the contact member is an elastic body.

16. The impact tool according to claim 14 , wherein the contact member is a rubber O-ring.

17. The impact tool according to claim 10 , wherein the contact member is a rubber O-ring.

18. An impact tool comprising:

a motor;

a hammer that is rotated by the motor;

an anvil configured to be struck by the hammer to rotate the anvil about a rotational axis;

a hammer case that houses the hammer;

a first bearing surrounding and rotatably supporting the anvil; and

a second bearing surrounding and rotatably supporting the anvil;

wherein:

the first bearing is a first one of a regular ball bearing, an angular contact ball bearing or a self-aligning bearing;

the second bearing is different one of a regular ball bearing, an angular contact ball bearing or a self-aligning bearing; and

the first and the second bearings are disposed within the hammer case.

19. The impact tool according to claim 18 , wherein:

the first bearing is a regular ball bearing;

the second bearing is an angular contact bearing; and

at least one intermediate washer is interposed between the regular ball bearing and the angular contact bearing.

20. The impact tool according to claim 19 , wherein the at least one intermediate washer directly contacts both the regular ball bearing and the angular contact bearing.