B3V

There are two dagger standards: eta UMa and eta Aur

Lesh68 lists Eta Aur as their primary B3V standard, with HD 178329 
as their secondary B3V standard. 

MK43, Garrison67, Hiltner69 & Garrison77 list Eta Aur (=HD 32630) as its B3V standard.

Walborn71 lists two B3V standards: Eta UMa & Eta Aur.

Cowley72 lists Eta Aur & Iot Her as B3V standards. 

Walborn90 shows Eta Hya (=HD 74280) as its B3V standard.

Skiff08 flaged three B3V standards: HD 120315 (MK73), HD 32630 (MK73), & HD 20365 (MK78).

<B-V>(B3V) = -0.181
<U-B>(B3V) = -0.653

Among the 9 good standards below: 
<B-V>(B3V) = -0.180 (+-0.006 stdev; N=9 standards)
<U-B>(B3V) = -0.650 (+-0.026 stdev; N=9 standards)

# Dagger Standards
HD 32630 = Eta Aur = HR 1641 = ALS 8168 
  B3V: MK43,JM53,Garrison67(stan),Lesh68(stan),Hiltner69(stan),Walborn71,MK73,Garrison77(stan),Garrison94
  M91: V=3.172+-0.008, B-V=-0.178+-0.009, U-B=-0.669+-0.005
  =>QBV=> (B-V)o=-0.182, (U-B)o=-0.659, E(B-V)= 0.004, T=17408.

HD 120315 = Eta UMa = Alcaid = HR 5191
  B3V: MK43,JM53,Walborn71,MK73,Walborn90,Garrison94,Garrison96
  M91: V=1.860+-0.009, B-V=-0.190+-0.007, U-B=-0.673+-0.017
  =>QBV=> (B-V)o=-0.181, (U-B)o=-0.653, E(B-V)=-0.009, T=17295.

# Primary Standards
HD 20635 = 29 Per = Cl Melotte 20 383 (alpha Per cluster)
  B3V: Cannon(B3),Roman50,Slettebak55,Heckmann58(B3),Jaschek64(major.),Lesh68,Petrie69,Morgan71,Jaschek78,MK78,Keenan85,Garcia89,GrayAtlas
  B4IV: Abt78
  B3IV: Miczaika51
  Appears to be an excellent standard
  M91: V=5.145+-0.013, B-V=-0.056+-0.005, U-B=-0.557+-0.009
  =>QBV=> (B-V)o=-0.175, (U-B)o=-0.631, E(B-V)= 0.119, T=16829.

HD 142883 = HR 5934 = HIP 78168  (J1558-2058)
  B3V: Bertiau58(B3:V),Morris61,Garrison67,Slettebak68,Hiltner69,Hill70,Garrison79(stan),Houk88
  B5: Cannon
  Skiff09: all 6 references all call it B3V. deZeeuw+99 Upper Sco member. Excellent standard?
  M91: V=5.853+-0.007, B-V=0.021+-0.005, U-B=-0.489+-0.010
  QBV: (B-V)o=-0.171, (U-B)o=-0.616, E(B-V)=0.192

HD 74280 = eta Hya = HR 3454
  B3V: JM53,Jaschek64(all),Jaschek78(JM53),Walborn90,Cannon(B3),Houk99(Garrison),Levenhagen06
  B2V: Russeil07
  B4V: Lesh68
  Agreement among Morgan/Garrison/Walborn/Houk/Cannon. Good standard. 
  M91: V=4.297+-0.008, B-V=-0.195, U-B=-0.735
  QBV: (B-V)o=-0.198, (U-B)o=-0.722, E(B-V)=0.003 (lowest reddening among B3V standards)

# Secondary Standards
HD 6300 = HR 302 = SAO 91988 = BD+50_212
  B3V: Cannon(B3),JM53,Hoffleit91,Jaschek64(all),Jaschek78(Lesh68)
  All published types are B3 or B3V, but no types since Lesh68. 
  M91: V=6.528+-0.013, B-V=-0.081+-0.010, U-B=-0.579+-0.061
  QBV: (B-V)o=-0.176, (U-B)o=-0.635, E(B-V)=0.095

HD 16908 = 35 Ari = HR 801 
  B3V: Cannon(B3),JM53,Jaschek64(all but one),Jaschek78(Lesh68)
  All published types are B3 (excepting a 1931 source), but no types since Lesh68.  
  M91: V=4.656+-0.012, B-V=-0.136+-0.005, U-B=-0.625+-0.005
  QBV: (B-V)o=-0.178, (U-B)o=-0.643, E(B-V)=0.042

HD 208057 = 16 Peg = HR 8356 
  B3V: JM53,Jaschek64(most),Jaschek78(Lesh68),Slettebak82,Cannon(B3),Mendoza58(B3)
  B6V: : Herman59
  In Jaschek82 catalog of Be stars, however only one published type (from 1949) uses "e"
  Good standard, but it might be a Be star?
  M91: V=5.073+-0.008, B-V=-0.169+-0.011, U-B=-0.680+-0.099 (big unc.)
  QBV: (B-V)o=-0.187, (U-B)o=-0.679, E(B-V)=0.018

HD 178849 = HIP 94043
  B3V: JM53,Jaschek78(Guetter68),Cannon(B3),O'Keefe41
  B5V: Abt81
  V=7.0, NErn of 14" common proper motion pair (companion is A0,V=8.40)
  M91: V=7.025+-0.025, B-V=-0.130+-0.010, U-B=-0.635+-0.005
  QBV: (B-V)=-0.182, (U-B)o=-0.659, E(B-V)=0.052

# Weak Standards
HD 191263 = HR 7700 = HIP 99234
  B3V: JM53
  B3IV: Jaschek78(Lesh68)
  B2.5V: Guetter68
  B2IV: Crampton71
  B5: Cannon
  Not great agreement after JM53 called this a standard. 

HD 218537 = HR 8808
  B3V: JM53,Jaschek78(Lesh68),Abt81,Cannon(B3)
  B2V: Guetter68
  B2.5V: Garrison70
  JM53 B3V standard, but Garrison called B2.5V. 

HD 178329 =
  B3V: JM53,Jaschek78(Lesh68(stan)),Hill77,Cannon(B3)
  B2V: Guetter68
  V=6.5. Only Lesh68 considered it a standard, otherwise OK?

HD 41753 = nu Ori = HR 2159 
  B3V: Houk,JM53
  B3IV: Jaschek78(Lesh68)
  B2: Cannon 
  B0(V): 1980ApJS...44..389B
  Jaschek64 types are mix of B3IV and B3V. 

HD 160762 = Iot Her
  B3V: JM53,Cowley72(stan),Jaschek64(most)
  B3IV: MK43,Lesh68,MK78
  B3: Cannon,Neubauer43
  JM53 noted "SB". Best considered "B3IV" standard. 

# Rejected Candidate Standard
Lam Tau
  B2V: Hill75
  B3V: Slettebak55,Garrison96
  B3IV+A: Levato75
  B3.0 + A3/4: Olson68
  B3: Cannon
  Unresolved binary. Inappropriate as standard. Not considered as standard in literature.