(CNN) - Golfers are meticulous in their planning for major tournaments.
From hours spent on the practice ranges and putting greens, to testing new clubs and equipment, no stone gets left unturned.
Louis Oosthuizen is no different. The South African golfer is competing at this year's Open Championship, the tournament he won in 2010 to record his only victory in a major.
Ahead of his second round at the unforgiving Carnoustie golf course, in which he carded an impressive round of even par in difficult conditions, Oosthuizen talked CNN Living Golf's Shane O'Donoghue through the contents of his bag.
It includes no less than 19 clubs, so spare a thought for his caddie Greg Hearmon.
"He's a strong boy!" Oosthuizen quips.
"We call him A-Grade," he laughs, pointing at Hearmon, his caddie for the Open 2018. "Because I've got two -- B-Grade is at home," he jokes, referring to Wynand Stander.
"I've got quite a few new toys here that I need to test out. I normally have a seven-wood in here as well, but I left that at home."
Oosthuizen knows just how vital having a talented caddie is to winning a major trophy.
His caddie at the time of his 2010 Open victory was Zack Rasego, who Oosthuizen was reportedly set to part ways with due to a string of bad performances.
But the pair clicked back into gear ahead of the week in St. Andrews and Oosthuizen recorded the greatest win of his career.
The 35-year-old now switches between Hearmon and Stander -- but neither ever choose what goes in the bag.
"Between him and Wynand they have a rule: They don't help with selecting clubs ... because that's when they can get fired!" he laughs.
"So that's my job."
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