202 F.3d 957 (7th Cir. 2000)
Richardson Electronics, Ltd., et al.,    Petitioners,v.Panache Broadcasting of Pennsylvania, Inc.,    Defendant-Appellee.
Nos. 99-8043 & 99-8044
In the  United States Court of Appeals  For the Seventh Circuit
Submitted November 24, 1999Decided January  31, 2000

Appeals from the United States District Court  for the Northern District of Illinois, Eastern  Division.  No. 90 C 6400--John A. Nordberg, Judge.
Before Posner, Chief Judge, and Manion and  Diane P. Wood, Circuit Judges.
Posner, Chief Judge.


1
We have before us  a request for permission to file an  interlocutory appeal under 28 U.S.C. sec.  1292(b). The request requires us to  consider the relation between that  section and Rule 23(f) of the Federal  Rules of Civil Procedure, which permits  interlocutory appeals from orders  granting or denying class certification.  Blair v. Equifax Check Services, Inc.,  181 F.3d 832 (7th Cir. 1999). Rule 23(f) becameeffective on December 1, 1998,  long after this suit was filed but before  the order sought to be appealed was  issued. Generally a new procedural rule  applies to the uncompleted portions of  suits pending when the rule became  effective, and we have no reason to  depart from the general principle in  regard to Rule 23(f).


2
The plaintiffs--radio stations and other  users of electron power tubes (EPTs)--  brought this class action suit in 1990  against manufacturers of the product,  alleging that the defendants were fixing  prices and otherwise violating the  federal antitrust laws to the harm of the  plaintiffs, who seek damages. On May 13,  over the defendants' objections, the  district judge certified a class of EPT  purchasers allegedly harmed by the  defendants' actions. Two months later the  defendants asked the judge to certify his  order of certification for immediate  appeal under section 1292(b). He granted  the motion in October and within the  limit of 10 days permitted by the statute  the defendants requested our permission  to take the appeal.


3
There is no time limit in the statute or  in any applicable rules for seeking the  district judge's permission to appeal  under 1292(b), in contrast to the 10-day  limit not here exceeded on seeking our  permission if the district judge grants  his, concurrent permissions being  required. But a district judge should not  grant an inexcusably dilatory request,  Weir v. Propst, 915 F.2d 283, 287 (7th  Cir. 1990); Ferraro v. Secretary of HHS,  780 F. Supp. 978 (E.D.N.Y. 1992); cf.  Marisol v. Giuliani, 104 F.3d 524, 529  (2d Cir. 1996), as this appears to be; if  he does, we'll refuse our permission to  appeal. In any event, no excuse for the  defendants' taking two months to appeal  has been offered except the patently  inadequate one that the case had been  "largely dormant" for nine years,  requiring the defendants' lawyer to  refamiliarize himself with it in the face  of a "pre-existing, conflicting  commitment to meet a deadline in another  case." In these circumstances, the delay  alone was sufficient grounds for us to  refuse our permission to appeal.


4
A harder question is whether the appeal  satisfies the criteria for a section  1292(b) appeal, which is whether the  order sought to be appealed presents a  controlling question of law as to which  there is a substantial ground for  disagreement and the resolution of which  may materially advance the completion of  the litigation. We shall not have to  answer that question, because it merges  into the important question presented by  the request for our permission to appeal,  which is the relation between section  1292(b), which as we said has no fixed  deadline for seeking the permission of  the district court to take an appeal, and  Rule 23(f), which imposes a deadline of  10 days from the date of the order sought  to be appealed, a deadline which (if  applicable) the defendants exceeded by  more than six weeks.


5
The question in this case that the  defendants argue, and the district judge  agreed, satisfies the criteria for a  section 1292(b) appeal is whether the  legal and factual questions common to the  certified class of EPT users predominate  over the individual questions, so as to  justify class treatment under Fed. R.  Civ. P. 23(b)(3), given that (according  to the defendants) the suit embraces  hundreds of different kinds of EPT. This  question seems rather too fact-specific  to be suitable for a 1292(b) appeal, but  the more significant point is that it  fits much more neatly into Rule 23(f).  The rule itself does not set forth  criteria for the exercise of our  discretion to entertain appeals from  class-certification cases. We endeavored  to formulate such criteria in Blair v.  Equifax Check Services, Inc., supra, 181  F.3d at 834-35; see also Jefferson v.  Ingersoll Int'l, Inc., 195 F.3d 894, 897  (7th Cir. 1999); Committee Note to Fed.  R. Civ. P. 23(f). They are whether an  immediate appeal is necessary to enable  meaningful appellate review of a decision  granting or denying class certification  or would advance the development of the  law governing class actions. The question  whether the heterogeneity of the products  sold by defendants in a price-fixing suit  should block class treatment because the members of the class buy a different mix  of the products is an unresolved question  of class-action law and so might justify  a Rule 23(f) appeal under Blair. Whether  it does or not, it seems to us that when  a class-certification order is an  arguable candidate for a Rule 23(f)  appeal, the appellants may not use  section 1292(b) to circumvent the 10-day  limitation in Rule 23(f).


6
We do not cast this conclusion as a rule  of statutory interpretation; it is  unnecessary, or at least premature, to  engage in that or any interpretive  exercise in order to solve the problem of  circumvention. We need only make clear to  bench and bar--and we take this  opportunity to do so-- that district  judges should not, and we shall not,  authorize appeal under 28 U.S.C. sec.  1292(b) when appeal might lie under Rule  23(f). Should a case arise in which a  class-certification order is appealable  under 1292(b) but not under 23(f),  perhaps because it presents an issue that  while it satisfies the criteria of the  statute does not involve the merits of  class certification, the appellant can  protect himself by seeking the district  judge's permission to take a 1292(b)  appeal at the same time that the  appellant asks us to entertain his appeal  under 23(f).


7
We need not, at least at this juncture,  consider whether Rule 23(f) may actually  supersede section 1292(b) in the area of  their overlap. Although judicially  promulgated rules are ordinarily trumped  by statutes rather than vice versa,  section 2072(b) of the Judicial Code  makes an exception for the case of  procedural and evidentiary rules  promulgated by the Supreme Court, a  category that of course includes Fed. R.  Civ. P. 23(f). We need not decide the  extent to which Rule 23(f) curtails the  operation of section 1292(b) as a matter  of law, however, since as a matter of  practice we can avoid conflict between  rule and statute in the manner set forth  above.


8
For the reasons explained, we decline to  permit the section 1292(b) appeal that  the defendants seek to take in this case.

