Don't know what with the Japanese, they produced the best or the better only for their own...... The rest of the World, get a somewhat toned down specs or dare I say a more inferior specs..... I thought "All men are created equal"....... Apparently, we are still long way to go after Apartheid, a long way from Martin Luther King's dream..... A World for all Mankind.
The 6306 divers are the third generation Seiko's recreation divers. They are after the 6217 and 6105's families. The elder brother of the 6309, the 6306 is a 150m diver that looks and feels identical to the big cushion-cased 6309, but was marketed only in Japan. Below is the case design diagram for 6306 and 6309.
Both of the 6306 diver's watches for domestic and the 6309 diver's watches for overseas were made in Suwa Seikosha from 1976, and 6306 diver's watches were put on the production first. The 6306 divers are much rarer to find than the 6309 because their production years were relatively short and they only catered for Japanese market only. 6306 divers was produced from 1976-1981.
Most basic specifications for 6306 and 6309 divers were the same. Both 6309 and 6306 divers shared the same case and both have the bi-directional non-locking bezel. Although from the appearance they looked almost identical but 6309 weighted 108 gm as compared to 102 gm of 6306. This maybe due to the fact that 6309 has a finer finishing; i.e. the case is well polished.
Look at the case back below.... it is certainly more appealing than the 6309. The finishing cosmetic quality is way beyond the 6309. Like 6309, this is also a screw in big crown.
The 6306 diver differs from the 6309 in that it used the cal. 6306 movement with 21 Jewels (as opposed to 6309's with 17 Jewels) and it has hacking feature. Another subtle difference, as you will notice, is the Kanji (Japanese) day wheel. Both 6306 and 6309 movements have quickset day-date and are running at 21,600 bph.
(photo taken from http://www.relojes-especiales.com )
Below is from 1980 Seiko's catalogue showing the 6306 automatic diver.....
Both 6309 and 6306 are magnificent timepieces. I just hope that one day, Seiko and all the Japanese Manufacturers would share their best products with the rest of the World.