Birmingham

This year: 1st in North Group with ten wins and four losses
Last year: Winners
Most runs: Varun Chopra, 326
Most wickets: Recordo Gordon, 21
Highest total: 242 for 2 v Derbyshire
Highest individual score: Brendon McCullum, 158 v Derbyshire

Key features: Reigning champions, they have won 16 of their last 20 games in the competition and, with an 80% win rate at Edgbaston since the start of 2014 (12 wins, three defeats), they have an excellent opportunity to become the first side to successfully defend the T20 title. While Brendon McCullum is unavailable - the club have high hopes he will be back in future seasons - Ian Bell returns at the top of the order and Chris Woakes is fit again after knee and hamstring problems. Perhaps a little light on runs in the group stages, they have compensated with an outstanding bowling attack which includes Jeetan Patel - arguably the best spinner in the competition - and Oliver Hannon-Dalby, who relishes bowling at the death. Some modest form in recent cricket suggests they are not in the best of form, but their T20 record is exceptional.

Key player: Rikki Clarke has the best economy rate of any bowler to have delivered five overs or more in this year's competition. Invariably taking the new ball, his control and variations at the top of the innings tend to put batsmen under pressure from the start - nobody has delivered more than his 142 dot balls in this year's competition - while he remains a free-scoring batsman happy either at the top or in the middle-order. As good a fielder as anyone in the county game, he gives the impression - at slip, in particular - that he could catch Lord Lucan.

The coach, Dougie Brown, says: "We have a poor record, historically, of reaching Finals Day. But I like to think we have reinvented ourselves in the last couple of years. We have such depth that we left Recordo Gordon - our top wicket-taker in the competition - out of our quarter-final team and the versatility that we can change our team between the semi and final if we play well enough to reach it. We trust our method, we trust each other and we have the experience and belief to fight back in any situation. Yorkshire have proved they are, by a distance, the best first-class side in the country and they have set the rest of us a benchmark, but hopefully we can become the first side to successfully defend the T20 title."

Hampshire

This year: 3rd in South Group with eight wins and six losses
Last year: Losing semi-finalists
Most runs: James Vince, 641
Most wickets: Chris Wood, 18
Highest total: 204 for 3 v Sussex
Highest individual score: Vince, 107* v Worcestershire

Key features: The winners of the competition in 2010 and 2012, Hampshire are contesting their sixth Finals Day in succession. Blessed with some strong top-order batting in the likes of Michael Carberry, James Vince and Adam Wheater, they also have an experienced seam attack - including Fidel Edwards and Yaisr Arafat - and some very good limited-overs spinners in Danny Briggs, Will Smith and 18-year-old legspinner Mason Crane. They look to be a side with the balance and strength to flourish whatever the conditions.

Key player: Vince is developing into a very good player. Aged 24, he has not only impressed with his captaincy but he has scored a century and four half-centuries and is averaging 58.27 in this year's competition. It is probably premature to think of him as a future England captain - he will have to prove himself as a batsman first - but he does have all the right credentials.

The coach, Giles White, says: "What's the secret to our consistency? Well, there's no great secret. We gave a group of young players an opportunity in 2010, they enjoyed early success which gave them confidence. They are in tune with one another and the needs of the side and while we have a strong top-order that can take the game away from the opposition, we also have a bowling attack with every base covered. In the past we were, perhaps, a bit reliant on spin, but now we have pace and experience and variety. As for Mason Crane... he's very exciting. These are early days, but every challenge we put before him - batting against pace or fielding under pressure - he just impresses us more."

Lancashire

This year: 4th in North Group with seven wins and six losses
Last year: Losing finalists
Most runs: Steven Croft, 460
Most wickets: Stephen Parry, 21
Highest total: 231 for 4 v Yorkshire
Highest individual score: Croft, 94* v Derbyshire

Key features: Are Lancashire the domestic version of South Africa? Certainly their record in the later stages of knockout competitions is poor though they came within an ace of winning their first T20 title last year. Already all but assured of promotion in the Championship, they have enjoyed a good 2015 with Steven Croft driving their progress in this competition with five half-centuries and 11 wickets. Ashwell Prince, with four half-centuries, has also done well, while Jos Buttler is available - and anyone who saw his match-winnings innings against Yorkshire will know how important that is - in between England commitments. But it might be their spinners who hold the key on an Edgbaston surface that has tended to help such bowlers in recent times: with Arron Lilley, Stephen Parry, Croft and Simon Kerrigan - who is an intriguing inclusion in the squad - all available, they should have the depth to cope with the loss of Kyle Jarvis with a broken hand. George Edwards come into the squad in his place.

Key player: The availability of James Faulkner is a "huge bonus" according to Ashley Giles. The Australia allrounder was expected to be absent on international duty by now but, after a drink-driving conviction and subsequent disciplinary action from Cricket Australia, he was not selected for the limited-overs section of the Ashes tour and extended his stay with Lancashire instead. With a bowling average of 13.10 and a batting average of 39.57 in this year's competition, he is the ideal player: an allrounder who relishes pressure and can win a game with bat and ball.

The coach, Ashley Giles, says: "It seems to me we play our best under pressure. But this is my first time at Finals Day, so I guess we'll find out. In many ways, the club is in a similar position to when I took over at Warwickshire: a great stadium and a good group of young players. The likes of Liam Livingston, Jordan Clark, Tom Bailey, Saqib Mahmood and Arron Lilley have come on in leaps and bounds and I'm very excited about the future. It took a while to get over the disappointment of the England coaching job, but I'm enjoying this very much and honestly not thinking about anything beyond it."

Northamptonshire

This year: 3rd in North Group with seven wins and five losses
Last year: Eliminated in the group stages
Most runs: Richard Levi, 406
Most wickets: Azharullah, 15
Highest total: 197 for 7 v Worcestershire
Highest individual score: David Willey, 100 v Sussex

Key features: Shahid Afridi returns - he landed on Friday afternoon - to boost a squad with several injury concerns. Allrounder Steven Crook has a damaged tendon in his right ankle and, while he will undergo a fitness test on Saturday morning, it seems the best he can hope for is a role as a batsman. Graeme White, the left-arm spinner, will also undergo a late fitness test after sustaining a side strain, though Adam Rossington and Olly Stone have been declared fit after recent doubts. The winners of the competition in 2013, Northants endured a horrid season in 2014 but have stabilised this year despite dire reports of the financial plight of the club and the imminent departure of several relatively high-profile players. For now, though, they have several dangerous players - not least the allrounders David Willey, Crook, Josh Cobb and Afridi - and a fine pair of bowlers in Rory Kleinveldt and Azharullah.

Key player: Willey might be unproven at international level, but at domestic level he is a match-winner with bat and ball. He thrashed a century off just 40 balls - the third-fastest ever in England - to help Northants to victory over Sussex in the quarter-final and, in the 2013 final, hit a 19-ball half-century and took a hat-trick as the club won their first silverware since 1992. With this possibly his final outing for the club where he was developed and where his father played before he moves to Yorkshire, he will be highly motivated to make it a memorable farewell.

The coach, David Ripley, says: "We feel we're the flag-bearers for the smaller counties, aren't we? It does sometimes seem that it's us against them and it is tough for us to compete with the consistency of some of the bigger sides in first-class cricket. But we do have several match-winners in our side and we know we have the potential to beat anybody if we play at our best. It has not been easy to concentrate on cricket with all the off-field stories going on, but we watched the DVD of us winning here on the way up in the bus and it reminded us of what a good side we are. We'll be sorry to see David Willey go, but he goes with our blessing: he has been a fine player for us and he's going to the best club in the country to progress his career. We all wish him well."