For any golfer, getting a hole-in-one is a momentous experience. For Japanese golfers, it can also be incredibly expensive.

Japanese custom requires the shooter of a hole-in-one to throw a lavish party for his or her friends. The cost of one such party could run as much as $10,000. To help soften the punch to the bank account, many Japanese golfers avail themselves with “hole-in-one insurance” policies.

Starting at $65 a year, the policies cover a party up to $3,000. Nearly 4 million Japanese amateur golfers maintain these policies. This amounts to nearly 40% of all the golfers in the nation.

First offered by Kyoei Mutual Fire and Marine Insurance Co. in 1982, the policies are now offered by at least 30 different firms. Since occurrences of holes-in-one are quite rare (once in every 10,700 rounds of golf), these policies tend to be quite profitable for the companies, raking in an estimated $220 million per year.

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Read more fun facts about Japan.