Strings on my DF-A12 matched reciprocal tuning instruments. 
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I've been using this set up ( the preferred version ) for a while now

The invoice details for ordering via stringsbymail.com us below

note: gauges are in inches.

1st   Db4 0.016  T
2nd   Ab3 0.024  T
3rd   Eb3 0.025  T
4th   Bb2 0.034  L / or 0.031 T (preferred)
5th   F2  0.042  L / or 0.039  T (preferred)
6th   C2  0.054  L
7th   Db1 0.095    / or Db1 0.098  H (preferred)
8th   Ab1 0.070  L
9th   Eb2 0.050  L / or Eb2 0.0437  HS (preferred)
10th  Bb2 0.034  L / or 0.031  T ( preferred)
11th  F3  0.022  L / or 0.25  T (preferred)
12th  C4  0.016  T

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L (La Bella silver plated copper singles)
T (Thomastik KR rope core)
H ( Hannabach doublebass guitar )
HS ( hannabach silver special )


names used for stringsbymail invoice
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1 x Hannabach Silver Special 8156MT - 6th string (E) Medium Tension (8156MT) 
1 x Hannabach 8416MT Doublebass Guitar 75cm Scale E String, Single (8416MT.75) 
1 x La Bella .054 Silver Wound Bass String, Single String (WS054) 
1 x La Bella .070 Silver Wound Bass String, Single String (WS070) 
2 x Thomastik-Infeld KN16 - 1st string (e) .016 nylon tape wound/rope core (KN16) 
1 x Thomastik-Infeld KN24 - 2nd string (b) .024 nylon tape wound/rope core (KN24) 
2 x Thomastik-Infeld KN25 - 3rd string (g) .025 nylon tape wound/rope core (KN25) 
2 x Thomastik-Infeld KR31 - 5th string (A) .031 (KR31) 
1 x Thomastik-Infeld KR39 - 6th string (E) .039 (KR39)