Carlin's Clement Novalak was again fastest in the third session of the day at Oulton Park, but only just, as Hillspeed's Sasakorn Chaimongkol ran him close, just 0.007s behind at the chequered flag.
Novalak followed up his pace in session two with another quick effort, while Chaimongkol found his speed after missing testing yesterday.
Chris Dittmann Racing's Ayrton Simmons was again a top-three contender, just 0.125s behind Chaimongkol, with Fortec's Johnathan Hoggard posting the fourth quickest time, 0.090s behind his old F4 rival.
Yet again, tiny margins separated the field, with Hoggard 0.015s ahead of Double R's Neil Verhagen, with his team mate Hampus Ericsson sixth and just 0.086s behind.
Douglas Motorsport's Kiern Jewiss was seventh, 0.020s behind Ericsson and 0.055s clear of Carlin's Kaylen Frederick. Jewiss's team mates Ulysse De Pauw and Benjamin Pedersen completed a top-10 separated by 0.747 seconds.
The final test session ahead of the race weekend is due to commence at 15.55.
BRDC British F3 Championship, Oulton Park Friday test session three top-10:
1. Clement Novalak, Carlin, 1m31.387s
2. Sasakorn Chaimongkol, Hillspeed, +0.007s
3. Ayrton Simmons, Chris Dittmann Racing, +0.132s
4. Johnathan Hoggard, Fortec Motorsports, +0.222s
5. Neil Verhagen, Double R Racing, +0.237s
6. Hampus Ericsson, Double R Racing, +0.323s
7. Kiern Jewiss, Douglas Motorsport, +0.343s
8. Kaylen Frederick, Carlin, +0.398s
9. Ulysse De Pauw, Douglas Motorsport, +0.617s
10. Benjamin Pedersen, Douglas Motorsport, +0.747s
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19 July 2019 - Verhagen tops opening Spa practice
18 July 2019 - Varrone returns to Hillspeed for majority of final rounds